Wikis are websites enabling multiple users to create and edit content. Although wikis can be created by single users, they are generally used for collaborative projects. A wiki is most useful when creating a community accessible site, where constructive criticism is encouraged. In general, wikis work well when you have a fairly limited number of people contributing content, and a larger body of readers.
A blog is an online journal that an individual creates. Blogs allow for a much tighter focus on editorial control. The editor can disable comments, for instance. Even with comments enabled, they typically are not shown when a visitor comes to the site – the visitor has to choose to view comments.
Both tools provide a platform for feedback – blogs do it in the form of comments, while wikis do it by letting users directly edit the contents of a given page.
Below is a lighthearted look at the differences between the two (not a political commentary!) Enjoy~