Hmm..
Boost threshold is an ecu setting where we allow a certain drift of boost pressure before we try to automate its repair.

IE:
Std Esc Cos has an overboost allowance target of 14psi between 3000 and 4300rpm.. anywhere between those speeds and teh ecu will allow an over boost of 6 psi to make 14psi as std. The threshold there is around 2 psi so if it hit 16 the active maps would drop boost valve duty cycle to get the boost back within its target pressure.

That help?