If you are not familiar with the unit of measurement:
1 oz-in = 0.00706 Nm
if you are not familiar with torque:
1 Nm torque translates to 1N of force at a radial distance from the shaft of the motor of 1 m. As 1N gravitational force corresponds to an approx. 0.1kg weight, 1 Nm torque can lift* 0.1kg weight 1m away from the shaft, or 1 kg weight 0.1m away ...
Efficiency is power output divided by power input. Electrical power, your input, is
P = IV \\
Mechanical power, your output, is
P = Fv \\
P = \tau \omega \\
that is, force times speed or torque times angular speed. If you are stalled, then your speed is zero. If your speed is zero then your power is zero and your efficiency is zero.
Electric motors designed for stall torque can handle stall torque just fine. One giveaway sign of high stall torque motors is forced cooling (cooling with a powered fan and not just a fan mounted passively on the axis of the motor). One of the issued with stalling motors is heat, as the stopped rotor does not facilitate and airflow and the winding are more ...