Hi Guys,
I have a general understanding of what a torque converter does. But what specifically does "stall speed" refer to?

Thanks in advance!

Stall speed is the RPM as which the motor would stall if the drive shaft couldn't rotate.

A close approximation is the "flash" speed. Roll along at low speed in low gear and stab the throttle. The RPM to which the tach jumps just before the MPH changes is the "flash" speed.