What is it?
Wikipedia is an online free-content encyclopedia project. It is written by volunteers and can be edited by anyone with access to the website. This may cause concern over reliability and accuracy, but can be a very good source of information on articles you may not be able to find anywhere else. Using the collaborative information from users world-wide does make a very interesting encyclopedia.
Because of access to just about anything imaginable, and the fact that they encourage you to create new pages and edit existing ones, I have become addicted to it.
Here are some pages I have worked on: