What term describes the pressure against which a pump must operate?

The term that describes the pressure against which a pump must operate is "head." In the context of fluid mechanics and pump systems, head refers to the height of a column of liquid that the pump is capable of lifting. It represents the energy per unit weight of fluid and is a critical factor in determining the performance of a pump.

When evaluating how effectively a pump can move water, the head provides essential information regarding the resistance the pump must overcome. This includes factors such as the elevation changes in the system and the friction losses within the pipes. Understanding head is crucial for selecting the appropriate pump for a specific application, as it ensures that the pump can deliver water to the required height and through the intended system without issue.

Other terms listed may relate to the behavior of fluids in systems but do not encompass the specific concept of pressure against which a pump operates in the same way that head does.