What is the term for the speed for best rate of climb?

The term for the speed for the best rate of climb is indeed represented by VY. This speed allows an aircraft to gain the maximum altitude in the shortest amount of time. When flying at VY, the aircraft has an optimal angle of attack, ensuring that it has the best performance in terms of climb rate.

In contrast, VX is the speed for the best angle of climb, which is focused on achieving the greatest altitude gain over the shortest horizontal distance rather than the shortest time. V2 refers to the takeoff safety speed, which is crucial during the initial climb away from the runway. VCL is not a standard aviation term related to climb speeds and does not apply in this context. Thus, VY is the correct answer, as it is specifically defined as the speed for best rate of climb, enabling pilots to maximize their vertical performance during ascent.