A flight plan is a document that outlines the intended route and details of an aircraft's journey. It includes information such as departure and arrival airports, waypoints, altitude, and estimated flight time. Flight plans are essential for air traffic control to ensure safe and efficient air travel. Pilots must file a flight plan before taking off, which can be done through various methods, including online systems or in person at an airport. The plan is then reviewed by air traffic controllers, who use it to monitor the flight and provide necessary guidance during the journey.