Plain English Meaning
A piece of equipment that lets heat pass from something hot to something cooler, while keeping the two completely separate.
Full Definition
A device that transfers heat from one fluid or gas to another without allowing the two to mix. In aircraft, a common example is a unit that routes hot engine exhaust through a sealed jacket, with cabin or carburetor air passing around the outside of that jacket to absorb heat for cabin warming or carburetor anti-icing.
Context Anchor
Seen in aircraft cabin heating, cooling, oil cooling, and some fuel and engine-related systems.
Derivation
From 'heat' (warmth, thermal energy) and 'exchanger' (something that swaps one thing for another). The name describes the function exactly: heat is swapped from one side to the other, but the two never touch.