A room, vehicle, or other space that is closed up while one or more people are smoking a lot inside it. The air becomes hazy and hard to breathe in, and stains every object and person in the space with the smell of the smoke.
This definition applies to legal and non-drug cigarettes and cigars, different and separate from a marijuana hotbox.
Nonsmoker: Ugh, this place is a total smokebox. Can't you take that outside or open a window?
Smoker: Fuck you.