Plain English Meaning

Warming up the engine from the outside before you try to start it, so the cold oil can move and the engine parts are not stiff or brittle when they begin to turn.

Full Definition

The application of external heat to a piston aircraft engine before starting in cold weather, used to warm the engine block, oil, and internal components so that oil can flow properly and the engine can start without damage.

Context Anchor

Seen during cold-weather preflight and engine starting procedures, especially when the airplane has been parked outside in low temperatures.

Derivation

From 'pre-' (before) and 'heat.' The word simply means heating something before it is used. The aviation point is that this heating happens before the start sequence, not after.