Social proof
Social proof (or informational social influence) is a psychological and social phenomenon wherein people copy the actions of others in choosing how to behave in a given situation. The term was coined by Robert Cialdini in his 1984 book Influence: Science and Practice. Social proof is used in ambiguous social situations where people are unable to determine the appropriate mode of behavior, and is driven by the assumption that the surrounding people possess more knowledge about the current situation. The effects of social influence can be seen in the tendency of large groups to conform. This is referred to in some publications as the herd behavior.