A power conditioner (also known as a line conditioner or power line conditioner) is a device intended to improve the quality of the power that is delivered to electrical load equipment. Like: UPS, Inverter, Servo Stabilizer, Automatic Voltage Stabilizer, Constant Voltage Stabilizer, Etc.
While there is no official definition of a power conditioner, the term most often refers to a device that acts in one or more ways to deliver a voltage of the proper level and characteristics to enable load equipment to function properly. In some uses, power conditioner refers to a voltage regulator with at least one other function to improve power quality (e.g. power factor correction, noise suppression, transient impulse protection, etc.)
The terms "power conditioning" and "power conditioner" can be misleading, as the word "power" here refers to the electricity generally rather than the more technical electric power.
Conditioners specifically work to smooth the sinusoidal A.C. wave form and maintain a constant voltage over varying loads.