Prisoner's Dilemma Definition

noun

In game theory, a situation in which, if each of the individuals involved chooses the most rational option for gaining his or her own ends, the least desirable outcome for all will necessarily result.

Webster's New World

Origin of Prisoner's Dilemma

From the common framing of the scenario as the story of two prisoners who are separately offered a plea bargain according to which the length of each prisoner's sentence depends on both his own decision to inform on the other and the other's decision to inform on him

From American Heritage Dictionary of the English Language, 5th Edition