This is slang for masturbating, the short way of saying it. Also the less embarrassing way of saying masturbating when speaking around adults and strangers.
ex. I caught him m.bating two times!
ex. I really enjoy a m.bating in the afternoon.
it is the short way of saying masterbate. it can also be said as m.bating as in masterbating.
my mom caught me m.bating.
i m.bate all the time.