姻亲 is the umbrella term for any relative gained through marriage — your spouse's blood relatives, your blood relatives' spouses, and so on. Compare with
血亲 (xuèqīn, blood relatives). In everyday speech people use specific terms like
公婆 (gōngpó, parents-in-law for a woman) or
岳父岳母 (yuèfù yuèmǔ, parents-in-law for a man) instead.
