Today’s term: Social facts
“A social fact is any way of acting, whether fixed or not, capable of exerting over the individual an external constraint”
From this, which has this nice explanation of why this is interesting:
The cohesion necessary for coordinated group effort can be only be explained by reference to “social facts”, those things that are true because everyone agrees they are true. Though it is tempting to regard such facts as weak or ephemeral, they are in fact both strong and persistent. You can take a car or a bus to work, but the fact that you get to drive your car but not the bus is a purely social phenomenon. Both the car and the bus have gas, steering, and brakes, but buses are governed by an elaborate, non-physical set of rules, ranging from the nature of property to the wearing of uniforms, rules that add up to your not being allowed to drive it.
which in turn I found via this entry on David Weinberger’s weblog: