Everything I read suggests they are different types of suspension systems. Here are a couple of explanations:

http://www.dieselbikes.com/articles/article_00002.htm
http://mtbiketrail.com/categories.html

Part of the reason I even know the difference is DH's incessant chatter about the Moots YBB. He saw one on the trail recently and has a bad case of bike lust.


ETA: Sorry for the threadjack. Back to our original programming.