A bid that enquires as to the quality of partner’s trump holding. In many systems, a bid of 5NT not preceded by 4NT asks about partner’s trump holding eg 2♣-pass-3♦-pass-5NT.
In Precision, it is quite common to play a single raise after a 1♣ opening and a positive response as a trump asking bid eg 1♣-Pass-1♠-Pass-2♠.