Plain English Meaning

The engine's oil is stored in its own tank outside the engine, not in a pan underneath it. Oil is pumped from the tank into the engine, then pumped back out to the tank again.

Full Definition

An engine lubrication system in which the oil supply is held in a separate external tank rather than in a reservoir built into the bottom of the engine. A pump draws oil from the tank, circulates it through the engine, and a second pump (the scavenge pump) returns the used oil from the engine back to the tank.

Context Anchor

Seen in aircraft engine oil system descriptions and during preflight oil quantity checks on engines that use a separate oil tank.

Derivation

"Sump" comes from the Middle English word for a pit or pool where liquid collects. A "wet sump" keeps oil pooled inside the engine itself; a "dry sump" keeps the engine's oil pan dry by sending the oil out to a separate tank.

Why Pilots Care

Maintains reliable oil supply and pressure during inverted or aggressive that would starve a .