is there any difference between external torque and torque?
Motor control engineer here (so my answer is not really physics-based):
Torque - EM torque developed by an electric machine
External torque - torque imposed by load (positive - generators such as gas/wind, negative - fans, compressors, etc.)
Draw a free body diagram. If the force producing the torque is external to a circle drawn around the body, the the force and its torque are external.
Separate names with a comma.