What term describes pressure that causes water to flow in the opposite direction than intended?

The term that describes pressure causing water to flow in the opposite direction than intended is back pressure. Back pressure occurs when the pressure in a plumbing system exceeds the pressure downstream, leading to a reversal of the intended flow direction. This phenomenon can create various issues, including contamination of the water supply or inefficient system performance. Understanding back pressure is crucial for plumbers, as it is essential to ensure that plumbing systems are designed to prevent it, particularly in situations involving pressure fluctuations or in systems with multiple components or appliances.