When talking about "trust fund children" or large savings it's common to hear the phrase "not touching the principal", which means that only the "earnings" from the money are spent, and the cash pile itself does not get smaller.
However I am not sure that this could possibly make sense: interest rates on bank account deposits are essentially zero, so it must mean earnings from the stock markets. There are stocks which pay dividends, but those are rather small, and it would take a stupendously large amount of money to live off dividends.
Another example is rise in stock market price - but that does not make sense either. If one owns 10 shares of company XXX, even if XXX stock price doubles every year, one would still have to sell shares to get anything - in this example any transaction would shrink the principal by 10%.
The only example where it does make sense is if the fund owns a number of properties and collects rent from them - in that case there should be very sizable earnings, but one does not hear about those examples often (I'm also quite curious why, it seems if one has $1 million or more, there's a lot of money to be made by investing in real estate, but with smaller funds, investment seems really hard).