Pluralistic ignorance
In social psychology, pluralistic ignorance is a situation in which a majority of group members privately reject a norm, but go along with it because they incorrectly assume that most others accept it. This is also described as "no one believes, but everyone thinks that everyone believes". In short, pluralistic ignorance is a bias about a social group, held by the members of that social group.
False consensus effect
The false-consensus effect can be contrasted with pluralistic ignorance, an error in which people privately disapprove but publicly support what seems to be the majority view (regarding a norm or belief), when the majority in fact shares their (private) disapproval. While the false-consensus effect leads people to wrongly believe that the majority agrees with them (when the majority, in fact, openly disagrees with them), the pluralistic ignorance effect leads people to wrongly believe that they disagree with the majority (when the majority, in fact, covertly agrees with them). Pluralistic ignorance might, for example, lead a student to engage in binge drinking because of the mistaken belief that most other students approve of it, while in reality most other students disapprove, but behave in the same way because they share the same mistaken (but collectively self-sustaining) belief. In a parallel example of the false-consensus effect, a student who likes binge drinking would believe that a majority also likes it, while in reality most others dislike it and openly say so.