A bliki is a marriage between a blog and a wiki. A blog is basically a series of posts by a person, much like an online version of a diary or a journal; a wiki is more like a website with interlinked pages that are easily and immediately editable (usually by anyone or by a restricted group).
Combining the two leads to many benefits.
Blogs profit from wiki features:
Wikis benefit from blog features:
Martin Fowler was probably the pioneer user of blikis. Visit Fowler's bliki for his interesting ideas on Agile, Ruby, and so on.
Today blikis are considered to be a part of Web 2.0.