Definition: Volt-Ampere Reactive (VAR) is a unit of measurement for reactive power in an AC (alternating current) electrical system. Reactive power represents the energy that oscillates between the source and the load without performing any real work. It is the imaginary part of apparent power and is crucial for maintaining voltage levels and stable operation of electrical grids.

History/origin: The concept of reactive power arose with the development of AC power systems in the late 19th century. Engineers realized that AC circuits not only delivered real power (measured in watts) but also involved reactive power due to the presence of inductive and capacitive elements. The term 'Volt-Ampere Reactive' was formalized to quantify this reactive power component.

Current use: VARs are extensively used in power system analysis, design, and control. Power companies monitor and manage reactive power flow to ensure voltage stability, minimize transmission losses, and optimize the efficiency of electrical grids. VAR compensation devices, such as capacitor banks and static VAR compensators (SVCs), are employed to regulate reactive power levels in the system.