Definition
A mass of material, usually metal with high thermal conductivity, that absorbs and dissipates unwanted heat away from a component to keep it within its safe operating temperature range.
Plain English
A piece of metal attached to something that gets hot, used to pull the heat away so the part doesn't overheat.
Context Anchor
Seen in aircraft electrical equipment, radios, engine cooling discussions, and maintenance descriptions where heat must be moved away from a part.
Derivation
From 'heat' (thermal energy) and 'sink' (a place where something drains away). Just as a kitchen sink is where water flows to be carried off, a heat sink is where heat flows to be carried off.
Why Pilots Care
Components that lose their heat sink path -- through poor mounting, dirt buildup, or blocked airflow -- can overheat and fail. This matters for radios, transponders, and other avionics that depend on heat sinks to stay reliable in flight.
Analogy
A metal spoon in hot soup acts a little like a heat sink: it pulls heat from the soup into the spoon and spreads it through the metal.
Intuition Check
A heat sink does not make heat disappear. It gives heat a path away from the part that would otherwise get too hot.
Example Sentence 1
The transponder is bolted to an aluminum plate that acts as a heat sink, carrying heat away from the unit during operation.
Example Sentence 2
During preflight the technician confirmed the heat sink on the alternator regulator had clear airflow.