What is the difference between the threshold voltage (Vth) and gate-emitter voltage (Vge) for IGBT devices?
How can I calculate Vth of an IGBT chip?
The gate-emitter voltage is just that, the voltage that happens to be across the gate to emitter terminals.
The threshold voltage is that gate-emitter voltage where the device starts to conduct, where "starts" is usually defined as some minimum collector current at some applied voltage. The datasheet should define what criteria exactly are used to define "starts to conduct".