Hi Scott
A joint venture is much the same as a 'partnership' in that two or more people or entities work together for mutually beneficial purposes. This might mean profit-sharing, co-promotion, building subscriber/membership lists, etc.
The biggest perk to JV's, in my opinion, is that it is incentive-driven work. You stand to make more money, or gain more exposure, than any other way that I know of. You can achieve more - and achieve it faster - with two (or more) professionals of different industries as they each focus on their specific talent for the venture.
Some resources:
Anyone else want to share resources or thoughts on Joint Ventures?