This word can be used in ANY sentence ever!
Jimmy: what do you wanna do today
John: Ur mom
A term used primarily by middle school boys whenever they have the chance to say it. Usually this phrase is not used in the right context and is overly said to the point that no one thinks it is funny.
Person 1: what are you doing tomorrow?
Person 2: haha ur mom
something u say when a person asks u a question or insults u.
dude1 : what r we doing today?
dude 2 : ur mom.
Teacher: Gracy, care to tell the class what we are doing for homework tonight?
Gracy: We're doing ur mom