A scottish phrase which means 'your mother'.Usually used as an insult, though is commonplace among neds as they do not feature the ability to speak properly.
Awright Cusick, a kicked yermaw's back door in last night.
Your mother:
Scottish adoption of the American insult, i.e. "Yo'mama so fat, Ben Kenobi said, 'Dang! That's no moon.'" Interestingly used in the film Terminator when Lt Traxler responds to Dt. Vuckovich's comment that he 'looks like shit' by simply saying "Yo' mama." The rest of the insult being implied.
Traditionally, during a conversational piece, a lot of Scots will leave the implication to the imagination of the receiver. Thus, many delivered insults are not acknowledged until such times as the receiver recounts what he/she just said or the methadone wears off. On average, many of the sharper Scots will respond with "No, No. That's your Maw that is." Which is a tip-of-the-hat to the popular Baddiel and Skinner sketch.