A social fact...

"A social fact is to be recognized by the power of external coercion which it exercises or is capable of exercising over individuals, and the presence of this power may be recognized in its turn either by the existence of some specific sanction or by the resistance offered against every individual effort that tends to violate it."

- Emile Durkheim, The Rules of Sociological Method

What does it mean to say there are "social facts"?