The standard definition often used when people explain what is meant by SEO is often something like

“Getting a web site found in the search engines.”

This is fairly accurate but only scrapes the service, SEO not only helps your site be found in the search engines but if done properly will increase the number of visitors you get and also increase the sales you make on your site.

Think about the way you and those you know use the internet, you don’t always type in the name of the site you are looking for, sometimes you do not know it other times you want to see what other sites are offering a similar service.
When you do this you tend to use the search engines, the most well known of these is Google, you type in a word or phrase and the search engine delivers back to you the results, now if your site is not in the top 10 you will not be on the first page of results.

If you are not on the first page of results you are much less likely to be found by potential visitors and customers, using search engine optimisation correctly can help you gain these top positions in the search engines.