Complex sentence: Stall torque is the torque which is produced by a device when the output rotational speed is zero, it may also mean the torque load that causes the output rotational speed of a device to become zero-i.e. to cause stalling.
Split into simpler sentences: Stall torque is the torque which is produced by a device when the output rotational speed is zero. It may also mean the torque load that causes the output rotational speed of a device to become zero-i.e. to cause stalling.