Search Engine Optimisation
SEO is "the process of improving the volume and quality of traffic to a web site from search engines", also known as improving your page rank. The desired result is that a search for your services will show your website as highly placed in the search rankings as possible.
The majority of SEO work is a task of analysing your web site content to ensure that it is written in the manner that your visitors will be searching for you. This can be performed on a project basis, or as an ongoing task (analysing website visitors each month, and reshaping parts of the website over time to draw in more and more relevant visitors).