Forum currency is vertual currency systems some forums have. Some forums let you buy or sell forum currency and in some other forums you can buy things from forum or other members of forum.

Each of these currency have a real money value. For example at Namepros.com their forum currecy equal to 0.02$ ( 1$ = 50 NP$). You can use this forum money to buy various things from forum members. Like at namepros you can buy doman names, Web hostings and also various services with NP$.

Each forum has different ways to let members earn forum money. In some forums you earn forum money when you post in that forum. in other forums you can buy forum money or earn from other members. There are forums which buy back their forum currency but not al forums do this.