Unpaid traffic may originate from different kinds of searches including image search, video search, academic search, news search, and industry-specific vertical search engines.
As an Internet Marketing strategy, SEO considers how search engines work, the computer-programmed algorithms that dictate search engine behavior, what people search for, the actual search terms or keywords typed into search engines, and which search engines are preferred by their targeted audience. SEO is performed because a website will receive more visitors from a search engine when websites rank higher on the search engine results page (SERP). These visitors can then potentially be converted into customers.
History
Webmasters and content providers began optimizing websites for search engines in the mid-1990s, as the first search engines were cataloging the early web. Initially, all webmasters only needed to submit the address of a page, or URL, to the various engines, which would send a web crawler to crawl that page, extract links to other pages from it, and return information found on the page to be indexed. The process involves a search engine spider downloading a page and storing it on the search engine's server. A second program, known as an indexer, extracts information about the page, such as the words it contains, where they are located, and weight for specific words, as well as all links the page contains. All of this information is then placed into a scheduler for crawling at a later date.
Website owners recognized the value of a high ranking and visibility in search engine results, creating an opportunity for both white-hat and black-hat SEO practitioners. According to industry analyst Danny Sullivan, the phrase "Search Engine Optimization" probably came into use in 1997. Sullivan credits Bruce Clay as one of the first people to popularize the term.
Early versions of search algorithms relied on webmaster-provided information such as keyword meta tags or index files in engines like ALIWEB. Meta tags provide a guide to each page's content. Using metadata to index pages was found to be less than reliable, however, because the webmaster's choice of keywords in the meta tag could potentially be an inaccurate representation of the site's actual content. Flawed data in meta tags, such as those that were inaccurate or incomplete, created the potential for pages to be mischaracterized in irrelevant searches.
Web content providers also manipulated some attributes within the HTML source of a page in an attempt to rank well in search engines. By 1997, search engine designers recognized that webmasters were making efforts to rank well in their search engines and that some webmasters were even manipulating their rankings in search results by stuffing pages with excessive or irrelevant keywords. Early search engines such as Altavista and Infoseek, adjusted their algorithms to prevent webmasters from manipulating rankings.
By heavily relying on factors such as keyword density, which were exclusively within a webmaster's control, early search engines suffered from abuse and ranking manipulation. To provide better results to their users, search engines had to adapt to ensure their results pages showed the most relevant search results, rather than unrelated pages stuffed with numerous keywords by unscrupulous webmasters. This meant moving away from heavy reliance on term density to a more holistic process for scoring semantic signals. Since the success and popularity of a search engine are determined by its ability to produce the most relevant results to any given search, poor quality or irrelevant search results could lead users to find other search sources. Search engines responded by developing more complex ranking algorithms, taking into account additional features that were more difficult for webmasters to manipulate.
Companies that employ overly aggressive techniques can get their client websites banned from the search results. In 2005, the Wall Street Journal reported on a company, Traffic Power, which allegedly used high-risk techniques and failed to disclose those risks to its clients. Wired magazine reported that the same company sued blogger and SEO Aaron Wall for writing about the ban. Google's Matt Cutts later confirmed that Google did ban Traffic Power and some of its clients.
Some search engines have also reached out to the SEO industry and are frequent sponsors and guests at SEO conferences, webchats, and seminars. Major search engines provide information and guidelines to help with website optimization. Google has a Sitemaps program to help webmasters learn if Google is having any problems indexing their website and also provides data on Google traffic to the website. Bing Webmaster Tools provides a way for webmasters to submit a sitemap and web feeds, allows users to determine the "crawl rate", and track the web pages index status.
In 2015, it was reported that Google was developing and promoting mobile search as a key feature within future products. In response, many brands began to take a different approach to their internet marketing strategies.
Relationship with Google
In 1998, two graduate students at Stanford University, Larry Page and Sergey Brin, developed "Backrub", a search engine that relied on a mathematical algorithm to rate the prominence of web pages. The number calculated by the algorithm, PageRank, is a function of the quantity and strength of inbound links. PageRank estimates the likelihood that a given page will be reached by the random web surfer.
Page and Brin founded Google in 1998. Google attracted a loyal following among the growing number of internet users, who liked its simple design. Off-page factors (such as PageRank and hyperlink analysis) were considered as well as on-page factors (such as keyword frequency, meta tags, headings, links, and site structure) to enable Google to avoid the kind of manipulation seen in search engines that only considered on-page factors for their rankings. Although PageRank was more difficult to game, webmasters had already developed link-building tools and schemes to influence the Inktomi search engine, and these methods proved similarly applicable to gaming PageRank. Many sites focus on exchanging, buying, and selling links, often on a massive scale. Some of these schemes, or link farms, involved the creation of thousands of sites or the sole purpose of link spamming.
By 2004, search engines had incorporated a wide range of undisclosed factors in the algorithms they used to rank pages. Some SEO practitioners have studied different search engine optimization approaches and shared their opinions. Patents related to search engines can provide information to understand search engines better. In 2005, Google began personalizing search results for each user. Depending on their history of previous searches, Google crafted results for logged-in users.
In 2007, Google announced a campaign against paid links that transfer PageRank. On June 15, 2009, Google disclosed that they had taken measures to mitigate the effects of PageRank sculpting by use of the nofollow attribute on links. Matt Cutts, a well-known software engineer at Google, announced that Google Bot would no longer treat any no-follow links, in the same way, to prevent SEO service providers from using nofollow for PageRank sculpting. As a result of this change, the usage of nofollow led to the evaporation of PageRank. To avoid the above, SEO engineers developed alternative techniques that replace no-followed tags with obfuscated JavaScript and thus permit PageRank sculpting. Additionally, several solutions have been suggested, including iframes, flash, and JavaScript.
In December 2009, Google announced it would be using the web search history of all its users to populate search results. On June 8, 2010, a new web indexing system called Google Caffeine was announced. Designed to allow users to find news results, Forum posts, and other content much sooner after publishing than before, Google Caffeine was a change to the way Google updated its index to make things show up quicker on Google than before.
According to Carrie Grimes, the software engineer who announced Google Caffeine for Google, "Caffeine provides 50 percent fresher results for web search than our last index".
Historically site administrators have spent months or even years optimizing websites to increase search rankings. With the growth in popularity of social media sites and Blogs, the leading engines made changes to their algorithms to allow fresh content to rank quickly within the search results.
In February 2011, Google announced the Panda update, which penalizes websites containing content duplicated from other websites and sources. Historically websites have copied content from one another and benefited in search engine rankings by engaging in this practice. However, Google implemented a new system that punishes sites whose content is not unique. The 2012 Google Penguin attempted to penalize websites that used manipulative techniques to improve their rankings on the search engine. Although Google Penguin has been presented as an algorithm aimed at fighting web spam, it focuses on spammy links by gauging the quality of the sites the links are coming from. The 2013 Google Hummingbird update featured an algorithm change designed to improve Google's natural language processing and semantic understanding of web pages.
Hummingbird's language processing system falls under the newly recognized term of "conversational search", where the system pays more attention to each word in the query to better match the pages to the meaning of the query rather than a few words. With regards to the changes made to search engine optimization, for content publishers and writers, Hummingbird is intended to resolve issues by getting rid of irrelevant content and spam, allowing Google to produce high-quality content and rely on them to be "trusted" authors.
In October 2019, Google announced they would start applying BERT models for English language search queries in the US. Bidirectional Encoder Representations from Transformers (BERT) was another attempt by Google to improve their natural language processing, but this time to better understand the search queries of their users. In terms of search engine optimization, BERT intended to connect users more easily to relevant content and increase the quality of traffic coming to websites that are ranking in the Search Engine Results Page.
Methods
Getting Indexed
The leading search engines such as Google, Bing, and Yahoo! use crawlers to find pages or their algorithmic search results. Pages that are linked from other search engine-indexed pages do not need to be submitted because they are found automatically. The Yahoo! Directory and DMOZ, two major directories that closed in 2014 and 2017 respectively, both required manual submission and human editorial review. Google offers Google Search Console, for which an XML Sitemap feed can be created and submitted for free to ensure that all pages are found, especially pages that are not discoverable by automatically following links in addition to their URL submission console. Yahoo! formerly operated a paid submission service that guaranteed to crawl for a cost per click, however, this practice was discontinued in 2009.
Search engine crawlers may look at several different factors when crawling a site. Not every page is indexed by search engines. The distance of pages from the root directory of a site may be a factor in whether or not pages get crawled.
Mobile devices are used for the majority of Google searches. In November 2016, Google announced a major change to the way they are crawling websites and started to make their index mobile-first, which means the mobile version of a given website becomes the starting point for what Google includes in their index. In May 2019, Google updated the rendering engine of their crawler to be the latest version of Chromium (74 at the time of the announcement). Google indicated that they would regularly update the Chromium rendering engine to the latest version. In December 2019, Google began updating the User-Agent string of their crawler to reflect the latest Chrome version used by their rendering service. The delay was to allow webmasters time to update their code that responded to particular bot User-Agent strings. Google ran evaluations and felt confident the impact would be minor.
Preventing Crawling
To avoid undesirable content in the search indexes, webmasters can instruct spiders not to crawl certain files or directories through the standard robots.txt file in the root directory of the domain. Additionally, a page can be explicitly excluded from a search engine's database by using a meta tag specific to robots (usually ). When a search engine visits a site, the robots.txt located in the root directory is the first file crawled. The robots.txt file is then parsed and will instruct the robot as to which pages are not to be crawled. As a search engine crawler may keep a cached copy of this file, it may on occasion crawl pages a webmaster does not wish to crawl. Pages typically prevented from being crawled include login-specific pages such as shopping carts and user-specific content such as search results from internal searches. In March 2007, Google sunsetted the standard (and open-sourced their code) and now treats it as a hint, not a directive. To adequately ensure that pages are not indexed, a page-level robot's meta tag should be included.
Increasing Prominence
A variety of methods can increase the prominence of a webpage within the search results. Cross-linking between pages of the same website to provide more links to important pages may improve its visibility. Page design makes users trust a site and want to stay once they find it. When people bounce off a site, it counts against the site and affects its credibility. Writing content that includes frequently searched keyword phrases to be relevant to a wide variety of search queries will tend to increase traffic. Writing content to keep search engines crawling back frequently can give additional weight to a site. Adding relevant keywords to a web page's metadata, including the title tag and meta description, will tend to improve the relevancy of a site's search listings, thus increasing traffic. URL canonicalization of web pages accessible via multiple URLs, using the canonical link element or via 301 redirects can help make sure links to different versions of the URL all count towards the page link's popularity score, impacting the credibility of a website.
White Hat vs Black Hat Techniques
SEO techniques can be classified into two broad categories: techniques that search engine companies recommend as part of good design ("white hat"), and those techniques of which search engines do not approve ("black hat"). Search engines attempt to minimize the effect of the latter, among them Spamdexing. Industry commentators have classified these methods and the practitioners who employ them as either white-hat SEO or black-hat SEO. White hats tend to produce results that last a long time, whereas black hats anticipate that their sites may eventually be banned either temporarily or permanently once the search engines discover what they are doing.
An SEO technique is considered a white hat if it conforms to search engines' guidelines and involves no deception. As the search engine guidelines are not written as a series of rules or commandments, this is an important distinction to note. White hat SEO is not just about following guidelines but is about ensuring that the content a search engine indexes and subsequently ranks is the same content a user will see. White hat advice is generally summed up as creating content for users, not for search engines, and then making that content easily accessible to the "online spider" algorithms, rather than attempting to trick the algorithm from its intended purpose. White hat SEO is in many ways similar to web development that promotes accessibility, although the two are not identical.
Black hat SEO attempts to improve rankings in ways that are disapproved of by the search engines or involve deception. One black hat technique uses hidden text, either as text colored similar to the background, in an invisible div, or positioned off-screen. Another method gives a different page depending on whether the page is being requested by a human visitor or a search engine, a technique known as Cloaking. Another category sometimes used is grey hat SEO. This is in between the black hat and white hat approaches, where the methods employed avoid the site being penalized but do not act to produce the best content for users. Grey hat SEO is entirely focused on improving search engine rankings.
Search engines may penalize sites they discover using black or gray gat methods, either by reducing their rankings or eliminating their listings from their databases. Such penalties can be applied either automatically by the search engine's algorithm or by a manual site review. One, however, quickly apologized, fixed the offending pages, and was restored to Google's search engine results page.