Definition
A high-pressure pump used in a fuel injection system to deliver a precisely metered quantity of fuel to each cylinder of a reciprocating engine, or to the fuel discharge nozzles of a turbine engine, at the correct pressure and timing for proper combustion.
Plain English
A pump that pushes fuel under pressure into the engine in measured amounts, so each cylinder gets exactly the right amount of fuel at the right time.
Context Anchor
Seen in aircraft engine fuel-system descriptions, maintenance records, and troubleshooting for rough running or poor fuel flow.
Derivation
From Latin 'injicere', meaning 'to throw in' (in- 'into' + jacere 'to throw'). The pump 'throws' fuel into the induction system or combustion chamber, which is exactly what it does mechanically -- forcing fuel in under pressure rather than relying on suction, as a carburetor does.
Why Pilots Care
Reliable operation prevents power loss, rough running, or engine damage from incorrect fuel delivery.
Intuition Check
Do not read this as just any fuel pump. In this context, an injection pump is the pump that serves the fuel-injection system and helps get fuel sprayed into the engine.
Example Sentence 1
The injection pump on a fuel-injected engine delivers fuel directly to each cylinder, so there is no carburetor to ice up.
Example Sentence 2
A failing injection pump can cause the engine to run lean and overheat during high-power climbs.