A Wiki Is Best Defined As

A wiki is best defined as:

A) a web site that typically acts as brokers for advertisers and web sites.
B) a smaller version of the banner that often look like an icon and usually provide a link to an advertiser's landing page.
C) a reverse chronological journaling site.
D) a user-collaborated content site, typically text in nature.
E) a little billboard that spreads across the top or bottom of the web page.