Plain English Meaning
The slippery fluid that flows through the engine to keep its moving parts lubricated, cooled, and clean.
Full Definition
A petroleum-based or synthetic lubricant circulated through an aircraft engine to reduce friction between moving parts, carry away heat, seal piston rings, flush contaminants to the filter, and inhibit corrosion of internal components.
Context Anchor
Encountered during preflight oil checks, oil servicing, maintenance, and cleanup after leaks or spills.
Why Pilots Care
Using the correct type and quantity of engine oil prevents excessive wear, overheating, and sudden engine failure; the wrong oil can destroy an engine in flight.