Plain English Meaning
When one engine is pushing harder than the other, the airplane wants to swing and roll toward the weaker side. The pilot has to use rudder and aileron to keep it flying straight.
Full Definition
A condition in a multiengine airplane in which the thrust produced on one side of the aircraft is greater than the thrust produced on the other, creating a yawing and rolling tendency toward the side with less thrust. It most commonly occurs when one engine fails or is producing reduced power while the other engine continues to produce full or higher power.
Context Anchor
Encountered in multiengine training, especially when discussing engine failure, takeoff performance, and control of the airplane after one engine loses power.