A first solo flight is when a new aircraft pilot completes a short flight, including a takeoff and landing, by themselves. Achieving this milestone is known as soloing. In a more general sense, a "solo flight" or "solo time" refers to any flight time when a "pilot is the sole occupant in the aircraft."[1]
When piloting an aircraft solo, a pilot must not only fly and navigate the machine competently, but must also manage unpredictable developments, such as mechanical failure or bad weather, without aid from outside sources (most air traffic controllers are not pilots and may not be contactable anyway).