Emergency landing is a landing of an aircraft in a state of emergency. This does not necessarily happen on a runway. Emergency landings can be made in fields, on water surfaces, on trees, etc.

Emergency landing is the most general term to describe situations where an aircraft makes an abnormal touchdown. Various other terms are used to point out a specific aspect of the event:

• Forced landing is a situation where an aircraft unavoidably needs to land, usually regardless of terrain. A typical example of this is an airplane forced down by fuel exhaustion or failure of all engines.
• Precautionary landing is a situation where further flight is possible but inadvisable, i.e. in the judgement of flight crew, a hazard exists with continued flight. A common situation requiring a precautionary landing is a technical problem that is not serious enough to declare "Mayday" (e.g. navigation system degradation or loss of system redundancy) but the aircraft SOPs suggest that landing at the nearest suitable aerodrome should be made.
• Ditching is an emergency (forced or precautionary) landing on water. It includes occurrences by landplanes only.
• Belly landing is an emergency landing with the gear in the "up" position. This is usually caused by equipment malfunction (the gear cannot be extended or cannot reach locked position).
• Crash landing is a landing where the aircraft receives significant structural damage, e.g. due to a hard landing or a runway veer-off. Not all emergency landings are classified as crash landings - if the aircraft has remained intact (or has received minor damage) using the term would be inappropriate.

Therefore, emergency landing is a landing conducted in response to circumstances forcing the aircraft to land.