Torque convertor stall speed

Hi I was watching part of the show today, and While Dave and Sam were explaining Torque convertor stall speed, I thought I heard them describe it as ...." when the impeller and turbine were turning at the same speed ".... I had always thought that Stall speed was the rpm that the impeller would induce the tubine to turn but there would be a difference in speed causing a torque multiplication... Did I misunderstand what Dave and Sam were describing? thanks Mike