Essentially when a race horse is flying under the radar.
This could be because it has been running decently in high quality races and dropping down in grade, or coming from a good form line that most punters would overlook.
Mate 1: "What's your best roughie of the day?"
Mate 2: "Number 3 in race 6. Last few starts he's finished in the top five in Group company. Bookies have missed a trick with that low flyer. He's one of my racing tips of the year!"
