Definition
A unit of electrical energy equal to one watt of power used for one hour. It measures the total amount of work done or energy consumed, not the rate at which it is used.
Plain English
How much electrical energy is used when a one-watt device runs for one hour. It is a measure of total energy, not how fast the energy is being used.
Context Anchor
Seen in aircraft battery ratings, portable power supplies, and electrical equipment specifications.
Derivation
A direct combination: 'watt' (the unit of electrical power, named after the Scottish engineer James Watt) and 'hour' (the unit of time). The pairing tells you exactly what it measures: power multiplied by time, which equals energy.
Why Pilots Care
Tells how long an aircraft battery can supply essential power if the alternator fails.
Analogy
Like the total distance a car travels when driving at a steady speed for a fixed time, showing overall energy available rather than rate of use.
Intuition Check
Do not read watt-hour as the same thing as watt. A watt is a rate of using power; a watt-hour is the total amount used or stored over time.
Example Sentence 1
The aircraft's standby battery is rated at 24 watt-hours, giving the essential bus enough energy to run for a limited time after a generator failure.
Example Sentence 2
Before a long cross-country flight, the pilot checked that the backup battery held at least 800 watt-hours of usable energy.