Sartre’s existentialism makes frequent use of the term "bad faith." At its core, bad faith means self-deception. According to the existentialist, man is both radically free to act and radically responsible for those actions. This freedom is a scary thought, so people often pretend it’s not there – they deceive themselves and enter into bad faith. Bad faith takes all forms, but in No Exit it involves not owning up to one’s actions, not admitting the possibility of one’s own freedom, willingness to become an object in the eyes of another, and confining the self (or others) to social roles.
Though she appears to be Sartre’s voice in No Exit, Inez is actually in a permanent state of bad faith.