Noun. Slang word for money, especially that obtained by criminal, illegal, or generally shady practices, e.g. selling drugs,
prostitution, slave trading. Can also mean a pay check while working as an
illegal immigrant. Used first by people in
the black market and the Mafia.
Additionally, To 'give someone the mudsack' generally means to pay someone for doing something sneaky for you that you didn't want to do yourself.