Plain English Meaning
How the engine gets air into its cylinders so it can burn fuel. Either the engine simply breathes in air on its own, or a pump is used to push extra air in.
Full Definition
In an aircraft engine, aspiration refers to the method by which air is drawn into the cylinders for combustion. A naturally aspirated engine relies on atmospheric pressure alone to push air into the cylinders during the intake stroke, while a turbocharged or supercharged engine forces air in under higher pressure.
Context Anchor
Seen in fuel-system and engine discussions, especially when explaining how air and fuel get into a piston engine before burning.
Derivation
From the Latin 'aspirare', meaning 'to breathe upon' or 'to breathe in'. The use keeps that original sense: the engine is breathing in air, and the question is whether it breathes on its own or with help.