A specific room located in a public highschool, most likely a small office inside a band or music class complex. The purpose of a band room is similar to that of any other smokespot. Marijuana is commonly consumed in band rooms, usually in the form of vapor by use of a dab pen. Juuling is also commonplace in such an establishment.
"Band room sesh in lunch?"
"Fuck this class, let's skip to band room"