BB
Ball Bearing
The ball bearing is the ammunition used by airsoft. Usually 6mm in diameter, these small plastic balls weigh far less than half a gram each (usually 0.20g). 8mm BBs are also available for some replicas.
The benefit to the BB is that as it is spherical, it can be loaded or fired any way round. Unfortunately, this shape causes inherent instability during flight (an aerodynamically unstable object) and can cause slightly more unpredictable flight paths than with a pellet or bullet.
Airsoft ammunition - the whitish plastic balls 6mm in diameter that we shoot at one another. They come in various weights from 0.12g to 0.36g and may differ greatly in quality. There are usually never enough of them in your clip but no matter how well you clean your house, there is always a few in a corner or under the couch. There are also 'bio-degradable' BBs available and some brands even seem to do so (eventually). See also: tracer.