SEO stands for Search Engine Optimisation! There you go, that’s straight forward enough but not likely to be the answer you are looking for.
Let’s go back a little way, when the internet was a little less complex but still shrouded in mystery! If you wanted a website then you went down to ye old website shop and anything you wanted to do with the internet could be found there. Then Search Engines began to come into their own and become a mighty force. Human beings having an inquisitive nature then started to play with the search engines to see what made them tick, more importantly to see if they could propel certain things to the top of specific searches.
As with many things in this world, the humans started to push things to the limit and so the search engines implemented rules and guidelines in order to filter out bad stuff and create a more equal playing field for all.
Optimisation now centres on good web content which is relevant to a search engine query. The more that Google, Yahoo, Bing and the other engines produce filters to scour the internet for more relevant SERP (search engine results pages), the more important it is to optimise your website and its contents to accommodate these services.
Here is a short video by Matt Cutts of Google to give a brief description of how your searches happen!
An easy way to think about this would be ‘if a search term put into Google is the question, does your website have the answer?’ Now ask yourself how easy have you made it for the search engines to find that answer?