The load torque required at the gearbox or gearmotor output shaft.
The overall efficiency consists of the driving unit ( gearbox ) and the driven unit efficiency ( such as the chain or belt stage efficiency etc ).

see "Overall efficiency" calculation
Load Torque at the Motor Shaft
Variables   Units
TL Load torque lb-in
iT Total system reduction ratio  
ηT Overall efficiency %
TX Reflected load torque to input lb-in