Definition
In an AC electrical circuit, the ratio of true power (measured in watts) to apparent power (measured in volt-amperes). It is expressed as a decimal between 0 and 1, or as a percentage. Power factor reflects how much of the supplied electrical power is actually doing useful work, and how much is being stored and returned by inductive or capacitive components in the circuit.
Plain English
A number that shows how much of the electricity flowing into a device is actually being used to do work. A power factor of 1 means all of it is doing work. A lower number means some of the power is just sloshing back and forth in the circuit without producing useful output.
Context Anchor
Seen in aircraft electrical system discussions, especially with AC generators, inverters, motors, and electrical load limits.
Derivation
From 'power' (the rate of doing work) and 'factor' (a multiplier or ratio). The term names exactly what it is: the factor by which apparent power must be multiplied to get true power.
Why Pilots Care
A low power factor forces the alternator to work harder to supply the same useful power, which can cause overheating and reduced system capacity.
Intuition Check
Power factor is not a control that creates more power. It is a comparison number that shows how efficiently an AC circuit uses the power being supplied.
Example Sentence 1
The aircraft's AC generator is rated in volt-amperes because the power factor of the connected load determines how many of those volt-amperes become usable watts.
Example Sentence 2
A low power factor in the aircraft's AC bus required the generator to supply extra current for the same load.