Plain English Meaning

An engine lubrication setup where the oil lives in its own tank outside the engine, instead of pooling at the bottom of the engine itself. Pumps move the oil between the tank and the engine continuously.

Full Definition

An engine oil system in which the oil supply is stored in a separate external tank rather than in the engine's crankcase. A scavenge pump removes oil from the bottom of the engine and returns it to the tank, while a pressure pump draws oil from the tank and circulates it through the engine.

Context Anchor

Seen in aircraft engine oil system descriptions, preflight oil checks, and discussions of how the engine is lubricated.

Derivation

"Dry" because the engine's sump (the bottom collection area) stays dry — oil is pumped out as soon as it drains down, rather than being allowed to collect there. Knowing this makes the name self-explanatory: the sump is kept dry on purpose.

Why Pilots Care

Prevents oil starvation and loss of lubrication during aerobatic or inverted and provides steadier and cooling.