Definition
A landing performed with the wing flaps fully retracted, either by choice (as a training exercise) or by necessity (because the flap system has failed). Without flap extension, the airplane has a higher stall speed, requires a higher approach and touchdown speed, produces a flatter approach angle, and uses more runway than a normal flaps-extended landing.
Plain English
Landing the airplane without using the flaps. Because the flaps aren't there to help slow the airplane and steepen the descent, the approach is faster, flatter, and uses more runway than usual.
Context Anchor
Seen in emergency and abnormal procedures when the flaps will not extend, or during training to practice landing without flap help.
Derivation
Flap comes from an old word meaning a loose piece that moves back and forth. On an airplane, a flap is a movable panel on the wing that can be lowered for landing; no-flap simply means that panel is not lowered.
Why Pilots Care
The airplane must be flown at a higher approach speed and will require more runway to stop, raising the chance of a runway overrun if the pilot does not adjust the landing plan.
Intuition Check
No-flap does not mean the airplane cannot land. It means the pilot must land without the extra lift and drag the flaps normally provide.
Example Sentence 1
After the flap motor failed in the pattern, the pilot briefed a no-flap landing and chose the longest runway available.
Example Sentence 2
Instructors often have students practice no-flap landings so they can handle real flap problems safely.