Search Engine Optimization (SEO) is the adjusting of a website so
that it ranks well within a given Search Engine. The exact and
utmost objective of optimizing is to increase traffic (people visiting) to
a site. Therefore, by ranking high (usually within the Top 10 results) for
a given keyword or phrase will dramatically increase your traffic. Better
the position of a site on a search engine result page, more will be the
traffic to the site. So a SEO campaign always targets at getting an
advanced ranking position on major search engines like
Google,
Yahoo, and
MSN for some target keyword(s)
or phrases. 
clipped from: www.ecns.ltd.uk 