I've heard "в бошке" during a singing class, one was referring to the head, or a part of it. What does it exactly mean?
Dmitry is right, in Russian this is the meaning. But it's rude and offensive. Its disdainful connotations are particularly pronounced in its plural form.
The word originates from Turkic languages where the origin word incidentally also means
a head both as a body part and as a chief (person).
In the context of drugs usage
башка/бошка is a slang name for cannabis female flower head.