Plain English Meaning
The speed that lets the aircraft stay in the air the longest on the fuel it has, by burning fuel as slowly as possible. It is about time aloft, not distance covered.
Full Definition
The airspeed at which an aircraft burns the least amount of fuel per unit of time, allowing it to remain airborne for the longest possible duration on a given quantity of fuel. It corresponds to the speed where total drag is at its lowest, requiring the least power to maintain level flight.
Context Anchor
Seen in performance charts and in discussions of the region of reversed command, especially when comparing speeds for maximum time aloft versus maximum distance.
Derivation
‘Endurance’ comes from Old French endurer, meaning ‘to last’ or ‘to .’ In it carries that same sense: how long the aircraft can last in the air before running out of fuel.