If you ever wanted to know the difference between a blog and a wiki or if you have been encountered with this question and were at a loss to explain it in plain words, then check out this post by Mike Sansone. He shows several examples to illustrate the differences.
Here is a sample of his explanations.
Blog – a Talk Show with call-in guests (e.g., Bill O’Reilly) — while guests and callers can comment on the conversation, at the end of the day — it’s Bill’s show.
Wiki – a Talk Show with a panel (e.g., The View) — Everyone contributes to the conversation.
Link to Mike’s post What’s the Difference between a Blog and a Wiki?