The idea of the motor is very general, is can be unary or binary, here binary refers to the sign of the motion/force being applied to it, if a motor is unary it can only be affected by a positive force. A motor can apply anything from a spinning motion to a sliding motion, it is easy the realise that both of these can be binary but also unary if chosen. Whereas a rocket motor provide a thrust motion will most likely only be unary.