When generating hydropower, the head is a general term used to describe the distance that a given water source has to fall before the point where power is generated. Ultimately the force responsible for hydropower is gravity, so a hydroelectricity plant with a tall/high head can produce more energy than a similar plant with a short/low head. In short, a larger head allows water to fall a greater distance, which in turn allows more kinetic energy to accumulate. That energy is then harnessed by a water wheel or water turbine to create usable hydropower.