A WIKI IS A WEBSITE THAT YOU CAN EDIT ONLINE EASILY.
Whenever you want to modify a page, click on the “edit” button,
make your changes and save the page.
The modified page now replaces the previous version.
This make it easy to update the web site and have people contribute content.
Each version of the page is stored in the page history and can be reverted if needed.
A wiki is a dynamic generated website. You can also add apps so that your users can directly put in their page (for example):
You can also, if you are very smart, develop your own application. The xwiki cloud that we are using offers a lot of possibilities. It is an open source project and if you are a developper, you can really customize your wiki (almost) as you want.
If you have any questions or difficulties, post them as comments on this page.