Acceleration

Acceleration is used to mean two things. One is an increase in speed and the other is the rate of increase of speed, and its SI unit is rad s^-2. When we need to distinguish these two, we use “acceleration rate” or “rate of acceleration” when referring to the latter.
In Japanese, there are two terms: 加速 (acceleration), and加速度(rate of acceleration). Acceleration means speeding up and its reverse is deceleration; to specify the latter's rate we use “deceleration rate.”
The figure below shows how the rotor and the load are accelerated by the torque generated by the current when voltage is applied to the motor.