Definition
Reservoirs at the lowest point of a reciprocating engine where lubricating oil collects after circulating through the engine. In a wet-sump system, the sump stores the engine's main oil supply; in a dry-sump system, oil drains into a small sump and is then pumped to a separate external tank.
Plain English
The low point of the engine where oil drains down and collects after it has done its job of lubricating moving parts. Think of it as the engine's oil catch basin.
Context Anchor
Seen in discussions of aircraft piston engine lubrication, oil quantity, and preflight engine checks.
Derivation
Sump comes from Middle English and Dutch, meaning a pit or low place where liquid collects -- like the sump at the bottom of a well or basement. The engine borrows the same idea: the lowest point where oil naturally settles by gravity.
Why Pilots Care
Maintaining correct oil quantity in the sump ensures continuous lubrication; running low risks engine damage or failure.
Analogy
An oil sump is like the low basin under a machine where fluid naturally drains and collects before being used again.
Intuition Check
Do not think of oil sumps as waste drains. In this context, they are collection and storage areas for oil the engine still needs.
Example Sentence 1
Most light aircraft engines use a wet-sump system, so the oil sump under the crankcase holds the entire oil supply.
Example Sentence 2
In wet-sump engines the lubricating oil remains inside the oil sumps rather than being stored in an external tank.