Power Quality represents the quality of the power supply of an electrical network, also called voltage quality.
It is a concept that is part of the problem of electromagnetic compatibility, which characterizes the ability of a device or system to operate in its electromagnetic environment in a satisfactory manner and without producing intolerable electromagnetic disturbances for everything in that environment.
This concerns both the immunity of the equipment and the emission of the disturbances it may generate.
Power Quality concerns in particular the phenomena of harmonics, flicker, unbalance, voltage dips, overvoltages, etc.