What is the term for a vertical column of fluid?

The term for a vertical column of fluid is referred to as "head." In the context of fluid mechanics, "head" represents the height of a fluid column above a reference point, typically measured in units such as feet or meters. It indicates the potential energy available in the fluid due to its elevation. This concept is crucial in hydraulic calculations, as it helps determine how fluid moves under the influence of gravity and pressure.

The other terms mentioned are related to fluid properties but do not specifically describe a vertical column of fluid. For instance, the friction factor pertains to the resistance to flow due to friction in pipes, and viscosity level refers to the thickness or resistance of a fluid to flow. Density height is not a widely recognized term in fluid dynamics, making "head" the most appropriate choice in this context.