Well, basically, if I "run" the whole box (on a repair which would be the case applicable to your situation) and can't find a good pair - be it F1 or F2 - I'll make the call to cable maintenence and tell them that I need to DC a pair. They will take the info, and send a team out to clear *one* pair for the circuit in question (two pairs on a 4-wire circuits, obviously) putting the customer (you) back in service.
No clue on where the term came from, though.
Once again, good luck.
