Plain English Meaning
How many aircraft the system can push through a given place in a given amount of time. More throughput means more flights handled per hour.
Full Definition
In air traffic management, throughput is the number of aircraft that can be moved through a given point, route, airspace sector, or airport in a set period of time. Higher throughput means more aircraft handled per hour without compromising separation or safety.
Context Anchor
Seen in discussions of NextGen, air traffic flow, airport delays, and how new procedures help more aircraft move safely through the system.
Derivation
From English 'through' + 'put' — literally how much can be 'put through' something. Originally an industrial and computing term for how much material or data passes through a system per unit of time. In it carries the same idea: how many aircraft pass through a point or sector per hour.