Plain English Meaning
A planned landing the pilot decides to make early — before a small problem turns into an emergency — while the airplane is still flying normally and the pilot can pick a safe spot to land.
Full Definition
A premeditated landing, on or off an airport, made when continued flight is possible but inadvisable due to a developing problem such as deteriorating weather, low fuel, becoming lost, gradual mechanical trouble, or pilot fatigue. The landing is carried out while the airplane is still under full control and the pilot can choose the time and place.
Context Anchor
Used in emergency landing training when a pilot must decide whether to keep flying or land early while there is still time to choose a suitable place.