flash money noun money, especially in a bankroll, intended for impressing, not spending US
He had retrieved it and arrested Big Dog, taking him to the detectives who, since Big Dog was a pimp, and had a five-page rap sheet, decided to book him for robbery, impound his car, and book his roll of flash money as evidence. — Joseph Wambaugh, TheNew Centurions, p. 223, 1970