SEO = Search Engine Optimization
The term SEO can also refer to "search engine optimizers," a term adopted by an industry of consultants who carry out search engine optimization on behalf of clients, and by employees of site owners who may perform SEO services in-house. Search engine optimizers often offer SEO as a stand-alone service or as a part of a larger marketing campaign. Because effective SEO can require making changes to the source code of a site, it is often very helpful when incorporated into the initial development and design of a site, leading to the use of the term "Search Engine Friendly" to describe designs, menus, content management systems and shopping carts that can be optimized easily and effectively.
SEM = Search Engine Marketing
Search Engine Optimization is considered by many to be a subset of search engine marketing, a term used to describe a process of improving the volume or quality of traffic to a web site from search engines, usually in "natural" ("organic" or "algorithmic") search results.
Search Engine Optimization is marketing to people online ("visitors") by understanding how search algorithms work and what these visitors might search for, to help match those visitors with sites offering what they are interested in finding.
Marketing efforts may also be seen in more narrow vertical search engines involving areas such as local search.
The goal of site owners and consultants engaging in Search Engine Optimization is to entice qualified visitors to their website. The quality of visitor traffic can be measured by how often a visitor using a specific keyword phrase leads to a desired "conversion" action, such as making a purchase, viewing or downloading a certain page, requesting further information, signing up for a newsletter, or taking some other specific action.
What is involved in Search Engine Optimization?
Creating web pages with SEO in mind does not necessarily mean creating content more favorable to algorithms than human visitors. Some SEO efforts may involve optimizing a site's coding, presentation, and structure, without making very noticeable changes to human visitors, such as incorporating a clear hierarchical structure to a site, and avoiding or fixing problems that might keep search engine indexing programs from fully spidering a site.Other, more noticeable efforts, involve including unique content on pages that can be easily indexed and extracted from those pages by search engines while also appealing to human visitors.
Webmasters and content providers began optimizing sites for search engines in the mid-1990s, as the first search engines were cataloging the early Web.
Initially, all a webmaster needed to do was submit a page, or URI, 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. The process involves a search engine spider downloading a page and storing it on the search engine's own server, where a second program, known as an indexer, extracts various information about the page, such as the words it contains and where these are located, as well as any weight for specific words, as well as any and all links the page contains, which are then placed into a scheduler for crawling at a later date.
Site owners started to recognize the value of having their sites highly ranked and visible in search engine results, creating an opportunity for both "white hat" and "black hat" SEO practitioners. Indeed, by 1996, email spam could be found on usenet touting SEO services. The earliest known use of the phrase "search engine optimization" was a spam message posted on Usenet on July 26, 1997.
At first, search engines were supplied with information about pages by the webmasters themselves. Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag, or index files in engines like ALIWEB. Meta-tags provided a guide to each page's content. But indexing pages based upon meta data was found to be less than reliable, mostly because webmasters abused meta tags by including keywords that had nothing to do with the content of their pages, to artificially increase page impressions for their Website and increase their Ad Revenue. Cost Per Impression was at the time the common means of monetizing content websites. Inaccurate, incomplete, and inconsistent meta data in meta tags caused pages to rank for irrelevant searches, and fail to rank for relevant searches. Search engines responded by developing more complex ranking algorithms, taking into account additional factors including: