Haven't heard that term in years. It's a B-52 performance speed!
B52's don't rotate at takeoff, they unstick. It's similar to the definition of V1 speed. But it's more likely the speed at which the ass-end of the plane begins to fly.
It is at this time the airplane is capable of flight in ground effect. B52's utilize ground effect more than other airplanes I've ever flown. After unstick speed, an engine loss is handled in ground effect.
I fly my engine loss senarios exactly this way in 767s, for many reasons other than performance. But that's a whole other tread.
Do a google search of unstick and B-52s...you'll get more information.