Social proof is a type of conformity. When a person is in a situation where they are unsure of the correct way to behave, they will often look to others for cues concerning the correct behavior. When “we conform because we believe that other’s interpretation of an ambiguous situation is more accurate than ours and will help us choose an appropriate course of action,” it is informational social influence. This is contrasted with normative social influence wherein a person conforms to be liked or accepted by others.
Social proof often leads not only to public compliance (conforming to the behavior of others publicly without necessarily believing it is correct) but also private acceptance (conforming out of a genuine belief that others are correct). Social proof is more powerful when being accurate is more important and when others are perceived as especially knowledgeable. (Via Wikipedia.org)