The movement of a liquid, such as urine, in the opposite direction to normal. The word reflux is sometimes used to mean reflux nephropathy.

Nephropathy is a condition in which urine passes back up from the bladder, through the ureter, to the kidney, where it can cause infections. It occurs because a valve that normally prevents the backflow of blood from the bladder is faulty. Reflux nephropathy is one of the causes of kidney failure.