The word Gamma means "the third in a series" :
1.Alpha 2.Beta 3.Gamma
It is a "3rd release" before the final release of VFK. After Gamma comes Delta which means 4.
VFK Staff Said : The gamma is the second step of going to gold. The gold is when vfk is completely perfect and there are no bugs and all of the stuff have been completed. Gamma is like an almost complete and beta is the beginning of the virtual world.