Urban Dictionary defines a word war as "An occurrence in which two or more writers set a time limit, such as ten minutes, or thirty minutes, to write or type as fast as they can on a specific topic or to add onto their current novel. The person with the highest word count at the end of the time limit wins the word war." That's a pretty good definition. Word wars help writers meet deadlines such as that imposed by NaNoWriMo or push past tough parts of their novels.
I could use a word war. I've never actually participated in one, and I'm yet again (it happens quite a bit) in a writing slump. A challenge, anyone?