Plain English Meaning
The speed that gives you the most height gained per minute when flying a twin with one engine out. It's the speed you aim for to climb away from the ground as quickly as possible on the remaining engine.
Full Definition
In a multi-engine airplane with one engine inoperative, the airspeed that produces the greatest gain in altitude per unit of time. It is published in the Pilot's Operating Handbook and is commonly designated VYSE. It assumes the critical engine failed, the propeller on the failed engine is feathered or in the position specified by the manufacturer, and the airplane is configured per the manufacturer's procedure.
Context Anchor
Seen in multiengine airplane , , and airspeed discussions; it is commonly with the blue marking on the when that marking is installed.