Definition
An alternating-current (AC) electric motor designed to operate from two or more separate AC voltage supplies (phases) that are offset from each other in time. The phases are delivered through separate windings in the motor, and their staggered peaks create a continuously rotating magnetic field inside the motor that drags the rotor around with it.
Plain English
An electric motor that runs on more than one AC power line at once. Because the power lines peak at slightly different times, they produce a smooth, steadily turning magnetic pull that keeps the motor spinning evenly.
Context Anchor
Seen in aircraft maintenance and electrical-system discussions, especially when identifying motors or equipment that require three-phase AC power.
Derivation
From Greek 'poly-' meaning many, plus 'phase,' meaning a stage in a repeating cycle. So 'polyphase' literally means 'many phases' — the motor uses several AC supplies whose cycles are timed to peak one after another.
Why Pilots Care
Polyphase motors run more smoothly, start more reliably, and produce more power for their size than single-phase motors. That is why they are used for the heavier electrical loads on larger aircraft, and why three-phase AC power is a standard part of those electrical systems.
Analogy
Think of several people pushing a playground merry-go-round at evenly spaced moments. Each push arrives at the right time, so the motion stays smooth instead of jerky.
Intuition Check
Polyphase does not mean the motor has many physical sections. It means the motor is powered by two or more timed AC electrical phases.
Example Sentence 1
The aircraft's main hydraulic pump is driven by a three-phase polyphase electric motor powered from the AC bus.
Example Sentence 2
During inspection the technician verified the polyphase electric motor was receiving balanced three-phase power.