What's the difference between a blog and a wiki?

This is the question we all ask ourselves when we are starting out with Web 2.0 tools. The words blog, wiki, Twitter, ning - all sound the same. Although a deep understanding of the difference between these tools comes once we start using them, it's a good idea to look at some brief definitions.

(Taken from Wiki Walkthrough from Teachers First)

What can blogging do for learning?