Plain English Meaning
It is everything in the airplane that holds the fuel and moves it from the tanks to the engine in a clean, steady supply.
Full Definition
The complete set of components in an aircraft that stores fuel and delivers it from the tanks to the engine at the correct pressure and flow rate. A fuel system typically includes fuel tanks, lines, selector valves, strainers or filters, pumps (engine-driven and/or electric boost), a primer, and gauges that indicate quantity and pressure.
Context Anchor
You encounter this term during preflight inspection, engine starting, fuel tank selection, fuel checks, and discussions of how the engine receives fuel.
Derivation
Fuel comes from an older word meaning material used for burning. System comes from a Greek word meaning things placed together as an organized whole. Together, the term reminds you that this is not just the fuel tank; it is the whole organized setup that handles fuel for the airplane.