Flight Closed  is when you see your flight flashing "Closed" you have missed your flight. Once a flight has Closed, the door is shut, the Gate Agent is standing at the end of the Jetway steering it away from the aircraft so it can 'push back.'

Other definition:
Flight Closed is when you see your flight flashing "Closed". You have missed your flight. Once a flight has Closed, the door is shut, the gate agent is standing at the end of the Jetway steering it away from the aircraft so it can 'push back.'