Wiktionary
n. (context US English) A train station at which trains stop only on request.
WordNet
n. a small railway station between the principal stations or a station where the train stops only on a signal [syn: whistle stop, way station]
Usage examples of "flag stop".
We have no idea how many are really competition, and we don't know what's built into that house, but he has a flag stop in there, that we know.
There's a westbound stopping here in New Ulm today, around ten, and like you said, the flag stop of Sleepy Eye ain't but a few minutes west by rail.
Major de Spain and the rest of that old group, save your Cousin Ike and Boon, were gone now and (there was gravel now all the way from Jefferson to De Spain's flag stop) their inheritors switched off their automobile engines to the sound of axes and saws where a year ago there had been only the voices of the running hounds.
Competent witnesses said there was no question that the man of bronze was the leader of a gang of five vacant-eyed men who boarded the train at a flag stop.