Basically, SEO is the act of continually optimizing a web site to improve its placement for targeted keywords and thus increase traffic to the site and/or make the web site easier to be found.

First of all, there are a few different terms to be aware of. They are Search Engine Marketing, Search Engine Friendly, Search Engine Optimization, and Search Engine Advertising.

Search Engine Marketing is simply the umbrella term for anything that has to do with marketing via search engines.