Today, however, SEM is used to refer exclusively to paid search. According to Search Engine Land, Search Engine Marketing is “the process of gaining website traffic by purchasing ads on search engines.” Search Engine Optimization, on the other hand, is defined as “the process of getting traffic from free, organic, editorial or natural search results.”
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"). The 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.[50] 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.[51]
Ever heard of Maslow's hierarchy of needs? It's a theory of psychology that prioritizes the most fundamental human needs (like air, water, and physical safety) over more advanced needs (like esteem and social belonging). The theory is that you can't achieve the needs at the top without ensuring the more fundamental needs are met first. Love doesn't matter if you don't have food.
Keep resources crawlable. Blocking page resources can give Google an incomplete picture of your website. This often happens when your robots.txt file is blocking access to some or all of your page resources. If Googlebot doesn't have access to a page's resources, such as CSS, JavaScript, or images, we may not detect that it's built to display and work well on a mobile browser. In other words, we may not detect that the page is "mobile-friendly," and therefore not properly serve it to mobile searchers.
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 black hat and white hat approaches, where the methods employed avoid the site being penalized but do not act in producing the best content for users. Grey hat SEO is entirely focused on improving search engine rankings.
This relationship between rankings and clicks (and traffic) is strongest amongst the top 3 search results. However, changing layout of the search results pages is constantly changing, with the inclusion of Google’s Knowledge Graph data and the integration of Universal Search elements (SERP Features) like videos, maps and Google Shopping ads. These developments can mean that the top 3 organic rankings are no longer the 3 best positions on the SERP. This has been demonstrated in heatmap and eye-tracking tests.
The leading search engines, such as Google, Bing and Yahoo!, use crawlers to find pages for 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 which closed in 2014 and 2017 respectively, both required manual submission and human editorial review.[40] 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[41] in addition to their URL submission console.[42] Yahoo! formerly operated a paid submission service that guaranteed crawling for a cost per click;[43] however, this practice was discontinued in 2009.

On October 17, 2002, SearchKing filed suit in the United States District Court, Western District of Oklahoma, against the search engine Google. SearchKing's claim was that Google's tactics to prevent spamdexing constituted a tortious interference with contractual relations. On May 27, 2003, the court granted Google's motion to dismiss the complaint because SearchKing "failed to state a claim upon which relief may be granted."[68][69]
A website or URL’s ranking for keywords or keyword combinations varies from search engine to search engine. A domain may rank for a certain keyword in the top 3 on Bing, but not even be on the first page of the Google search results for the same keyword. Of course, the same is true of all search engines – Bing, Google, Yahoo and every other search engine uses its own method for calculating rankings and therefore ranks websites differently.

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 "spider" to "crawl" that page, extract links to other pages from it, and return information found on the page to be indexed.[5] The process involves a search engine spider downloading a page and storing it on the search engine's own server. A second program, known as an indexer, extracts information about the page, such as the words it contains, where they are located, and any 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.