Definition
A controlled emergency landing of an aircraft on water, performed deliberately when continued flight is not possible and no suitable land surface is reachable.
Plain English
Putting the airplane down on water on purpose because you can't make it to a runway or safe ground.
Context Anchor
You will see this term in emergency landing and glide discussions, especially when a power loss or other problem leaves water as the only practical landing surface.
Derivation
From the British military slang use of 'ditch' (originally a trench or channel) to mean any body of water -- particularly the English Channel, which RAF pilots called 'the ditch.' To 'ditch' an aircraft came to mean putting it down in the water.
Why Pilots Care
Proper ditching technique reduces structural damage and gives occupants time to evacuate safely.
Intuition Check
Ditching does not mean abandoning the airplane in the air or simply crashing into water. It means making the best controlled landing possible on water when safer options are not available.
Example Sentence 1
After the engine quit ten miles offshore, the pilot briefed the passengers and prepared for ditching.
Example Sentence 2
The training emphasized keeping the wings level during ditching so the airplane would stay upright on the water.