A joint venture is where two or more people come together to combine their skills, knowledge, products and marketing efforts to create a successful business, project or campaign.
You can see the Wikipedia definition here:
http://en.wikipedia.org/wiki/Joint_venture
Here is an example from my own experience.
I have a joint venture with my programmer for one of my web sites where I pay him a percentage of the income rather than paying him by the hour.
The benefits for him? He gets to build long term equity and earns more than he could by just billing by the hour.
The benefits for me? My programmer has major incentive to keep my systems up and running as he doesn't get paid unless they are working well.
Joint ventures need to be mutually beneficial to be successful.
Garland Coulson, "The E-Business Tutor"
http://www.ebusinesstutor.com/article.php?story=joint-venture-definition