n. Money acquired from one's parents that doesn't have to be repaid... or the borrower doesn't intend to repay even if they are supposed to.
Said in a smug way by the people who use the 'bank', as they think they've got free money from their parents.
However, the parents know it exists and use the phrase in an annoyed kind of way... Like they know that the BoMaD exists and that it isn't right, but they can't do anything about it.
The BBC programme of the same name showed that the BoMaD can last well into a person's 40s, provided their parents are still alive.
Person 2: "Hmm I dunno, I've no bus money or money for drinks or money for a brand new and expensive outfit or money to spend on other people or money to pay the strippers with or money to buy fat cigars or money to get a limo home with..."
Person 1: "Bank of mum and dad, man!"
Person 2: "Oh yeah! You're on then!"