EDIT:

This is copied directly from Wikipedia simply because i think it sums up Parrhesia and because it's awesome:

Michel Foucault developed the concept of parrhesia as a mode of discourse in which one speaks openly and truthfully about one's opinions and ideas without the use of rhetoric, manipulation, or generalization.[2] Foucault's use of parrhesia, he tells us, is troubled by our modern day Cartesian model of evidential necessity. For Descartes, truth is the same as the undeniable. Whatever can be doubted must be, and, thus, speech that is not examined or criticized does not necessarily have a valid relation to truth.

There are several conditions upon which the traditional Ancient Greek notion of parrhesia relies. One who uses parrhesia is only recognized as doing so if he or she holds a credible relationship to the truth, if he serves as critic to either himself or popular opinion or culture, if the revelation of this truth places him in a position of danger and he persists in speaking the truth, nevertheless, as he feels it is his moral, social, and/or political obligation. Further, in a public situation, a user of parrhesia must be in a social position less empowered than those to whom he is revealing.