What is meant by "residual" fuel in aviation terms?

In aviation terminology, "residual" fuel refers specifically to the fuel that remains in the tanks after the aircraft has been drained for maintenance or inspection. It is important because knowing how much residual fuel is left can affect weight calculations, fuel management, and overall safety. This leftover fuel can also impact the efficiency of the aircraft during operation and must be accounted for before the next flight to ensure compliance with weight and balance requirements.

The other options do not align with the definition of residual fuel. For instance, the idea of additional flight fuel refers to fuel intended for use during operations rather than what’s left behind. Excess fuel for safety sounds similar but refers more to reserves or contingency planning rather than what remains in the tanks after servicing. Lastly, fuel lost during transport is an entirely different concept related to fuel management and logistics, not about what is left in the aircraft after draining.