Meaning varies. That which is considered
lower-class,
visceral,
puerile,
uncultured.
Popular culture as opposed to
fine arts. It's usually
derogatory, but for no good reason:
Airplane! is certainly lowbrow rather than
highbrow, but it's one of my favorite movies. The perception of
comedy in general as lowbrow may be why
critics never seem to review
funny movies well.
Presumably meant to evoke the
image of a
Neanderthal's thick
brow.