1. The woman who gave birth to you and/or raised you.
2. An all-purpose insult, used to end a conversation, cover for the fact that you can't think of a witty comeback, or pwn somebody. When used in this sense, the implication is that your mom is sexually promiscuous, of below-average intelligence, grossly overweight, or any combination thereof. Does not necessarily have to make a lot of sense, e.g. 'Your mom goes to college!'
3. A ho.
Dick: '...therefore, your argument can be proven irrefutably incorrect.'
Jane: 'Your mom!'
Dick: 'Where's the remote control?'
Jane: 'I left it in your mom.'
Stephen Hawking: 'The whole history of science has been the gradual realization that events do not happen in an arbitrary manner, but that they reflect a certain underlying order.'
Dick and Jane: 'Your mom doesn't happen in an arbitrary manner!'