A rhetorical technique used (often by a neurotic undergraduate a with
a Yoko Ono tattoo) to deny the existence of
irrefutable fact. But this is not its original meaning:
Properly understood, a social construct is a thing that emerges as a result of social interaction. For instance, the price of gold is a social construct—it emerges from the market for gold as an
approximation of how society presently values gold in relation to another asset, usually currency.
Social constructs are no less "real" than the price of gold is "real." It's not as real as gold itself, but it's pretty damn real.