A little more context is need for the device this specification applies to to. It sounds very much like the device is controlled by PWM, and whatever it controls is guaranteed to off with an applied PWM of 5% duty cycle and below, and guaranteed to be on with an applied duty cycle of 10% or higher.
What happens in the 5-10% range is anyone's guess, probably the on/off switching threshold is simply somewhere in that range, but the device may have hysteresis built in causing a deadband.