A Bitch Session is where a bunch of friends gather and bitch about all the crap that should be elminated from the face of the Earth, i.e., Stupid people, events that sucked, wastes of time, etc. ad infinitum.
Whenever my friends and I get a break from rehearsal, we go into the back room and have a Bitch Session about all the shit that shouldn't go on during rehearsal, like the time available to have a Bitch Session.
A time dedicated to complaining, griping, bitching, moaning, and gnashing teeth. Generally a group activity, in which the participants complain about one evil or annoying person, or about their respective S.O.s, ex-S.O.s, families, professors, bosses, etc. The name derives from the verb "to bitch" as in "to complain loudly and profanely", not from the noun "a bitch", thus the participants may be male as well as female.
"Looks like Jim and Bob are over by the water cooler having a bitch session about the price of Gasoline."