The definition to call your mother to get her angry and stare at you confusedly. It is also a great alternative to 'bro' or 'dude'. Incredibly versatile.
To masturbate while sexually fantasizing about one's own mother.
Ignacio: I always feel so guilty after I momturbate on Friday nights.
Jose: You should, bro. That's nasty!
Ignacio: I know man, but she has such firm, voluptuous, mouth-watering knockers!
Jose: O_o