SEO, or Search Engine Optimization, is gearing an article, or any piece of text, in such a way that a keyword or phrase triggers the web page whenever a particular search is done.  What this means is that when someone types in a certain word to search on Yahoo or Google, or whatever search engine they use, an SEO article will be more likely to appear at the top of a search list than one that is not SEO based.  Finding good SEO writers is how many online businesses manage to succeed, by making sure their web site appears to customers before any competition.

To really understand SEO and how SEO works, you need to understand how the entire search engine process works as well.  For example, let's pretend that you were looking for information online about dog medicine.  "Dog medicine" is now your keyword.  After you type your keywords in and hit enter, the search engine you're using (be it Yahoo, Google, Netscape, or any of the others—they all work the same way) will scan the internet for any documents that contain the words "dog medicine."  Once it finds all the possible websites that match those keywords, the search engine then has to sort through the results (and for a really generic keyword, there could literally be millions or tens of millions of websites that contain those words) for the ones deemed "most relevant."  That phrase holds the key.  The only way for the search engine to decipher the more relevant articles from the less relevant ones is by the number of times that the words "dog medicine" shows up in an article.  An article that mentions those words ten times will always appear in front of an article that only mentions those words two or three times.

It's that simple.  An article that mentions a certain word a lot will be considered "more relevant" than one that doesn't.  That's the reason why a page selling a particular product often times mentions that product's name 10, 12, 15 times in a few paragraphs, because it is that type of SEO optimization that allows the web site to be at the top of any search.  Employers who want their website to be more visible will hire SEO writers to "pepper" any article with a certain term.  For example, this article would do well in a search on "SEO" since the phrase appears several times.  It is that type of writing that allows your website or article to go from "needle in a haystack" to "easy find."