Revivify is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Roll a d20 and add the number of creature cards in your graveyard that were put there from the battlefield this turn. 1—14 | Return all creature cards in your graveyard that were put there from the battlefield this turn to your hand. 15+ | Return those cards from your graveyard to the battlefield.