Definition - What does Head Loss mean?
Head loss refers to the measurement of energy dissipated in a system due to friction. It accounts for the totality of energy losses due to the length of a pipe and those due to the function of fittings, valves and other system structures.
Corrosionpedia explains Head Loss
Lower head loss in a given system is experienced when there is a reduced velocity often due to pipe friction. An increase in liquid velocity can be experienced due to a variety of reasons such as the reduction of pipe diameter. Such changes can be seen to be reflected as an increase in head loss due to an increase in system friction.