OPM

living off Other Peoples Money

(note how it sounds like "opium")

typically any money you spend that isn't from your own revenue/income or savings

often implies you're spending it more sloppily than if it were your own money

see related: Capital Market

cf Family Money, Stupid Money, Greater Fool, Trust Fund, Subsidy, Non-Profit, Grant Money, Asset Bubble, Patronage, Art Collector, Luxury Customer...

Do Economic Transition-s depend on OPM Subsidy to reach Escape Velocity?