What is Wiki? Its like asking what is a blog? well, people do and its truly in accordance with their constitutional right of freedom of speech (and testing patience); regardless of what we techies think of them.
Wikipedia says : “A Wiki or wiki (pronounced "wicky" or "weeky" or "viki") is a website (or other hypertext document collection) that allows any user to add content, as on an Internet forum, but also allows that content to be edited by any other user.“
Or say collaboration tool which works (because its browser based?) may be my bet for a description. Write your contents on the fly could be another bumper sticker for wiki. Or Microsoft's third Open Source Initiative FlexWiki is an implementation of Wiki...I don't think its a right definition since a definition shouldn't have the word itself in it. Oh well!
Flex wiki is Microsoft's open source project on sourceforge built using ASP.NET and C#.(Windows installer XML [WiX] and Windows C++ Template Library [WTL]) are the two other.
And yes, wikipedia rocks! For those who love to learn a new thing everyday, why one?
Links:
FlexWiki Open Source Project Has Microsoft Talking
Microsoft Unveils Third Open-Source Project