Plain English Meaning
The push or load created when a moving airplane is suddenly slowed or stopped. In a landing, it's the heavy thump the gear has to absorb when the airplane meets the runway.
Full Definition
The force that arises from an aircraft's mass resisting a change in motion. During landing, it is the downward force the airplane exerts on the landing gear as its descent is suddenly arrested by ground contact. The harder or faster the touchdown, the greater the inertia force transmitted through the gear and airframe.
Context Anchor
Encountered in hard landing discussions, especially when explaining why a fast or abrupt touchdown can stress the landing gear and airplane structure.