Hydrodynamic Transmissions
The torque produced by a fluid coupling is maximum when the output stage is stalled (i.e. is not rotating), the stall torque may also refer to the maximum output torque that a fluid coupling can produce without damage.
In the case of torque converters, the stall torque is close to or the same as the maximum output torque produced for a given input speed.
Read more about this topic: Stall Torque