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.Stalling is a condition when the motor stops rotating.This condition occurs when the load torque is greater than the motor shaft torque i.e. break down torque condition. In this condition the motor draws maximum current but the motor does not rotate.The current is called as Stalling current. Devices such as electric motors, steam engines and hydrodynamic transmissions produce torque under these conditions.