What is search engine optimization?

What exactly is seo or search engine optimisation.Is it just link building or does it go to higher levels of website optimisation?

It's a complex subject, and it depends partly on which search engine you're talkng about. I'd recommend doing some serious research after you determine what SE you're looking at.

Generally speaking, it's defined as manipulating website content to achieve a greater amount of natural search engine traffic.

For me, it includes both content publishing, load time optimization, and some notion of user experience improvements...because all the traffic in the world is useless if people don't like what's on your page, or find it confusing.

Search engine optimization is a process of making a site's content easier for search engines to understand, index, and rate. A SEO effort would usually involve making sure that all pages have unique and descriptive <title> tags and relevant <meta> tags, that headings are tagged as such (I.e., using <h1>-<h6> tags rather than styled paragraphs), that all images have descriptive "alt" attributes, etc. Sometimes, large portions of content are rewritten entirely to include certain keywords and/or statistically improbable phrases.

There's also a different kind of "SEO", which can be undertaken separately or in conjunction with the above. Multiple ghost sites are set up to do nothing but to point to pages on the site being "optimized" in an attempt to bring up its page rating (pages to which other pages refer are rated higher).

Hmm... FunAdvice ate my references to HTML tags... Never mind, here's a link to this answer as it was intended:

http://www.myvirtualdisplay.com/2008/02/06/what-is-search-engine-optimization/