A "pop-up" is an on-the-spot IFR clearance from Air Traffic Control (ATC), often granted without a pre-filed flight plan or briefing, serving as a vital safety option to avoid hazardous scud running.

Departing VFR to obtain an IFR clearance in the air is highly dangerous and should be avoided, especially at night, in marginal VFR conditions, or when terrain or clouds are present. Pilots must ...