A normal prisoner’s dilemma played repeatedly by the same participants. An iterated prisoner’s dilemma differs from the original concept of a prisoner’s dilemma because participants can learn about the behavioral tendencies of their counterparty.
Taobiz explains Iterated Prisoner's Dilemma
Since the game is repeated, one individual can formulate a strategy that does not follow the regular logical convention of an isolated round.
"Tit for tat" is a common iterated prisoner’s dilemma strategy.