fly-in noun 3fly in verb 2forms 5 noun3 •An informal gathering of private pilots and their aircraft at a prearranged airfield. •The bringing of a people to a place by air travel.IBM […] has staged to "fly-ins" of company executives to appeal to lawmakers. — 2018 •A method of application for roll materials by which the dry sheet is set into the bitumen or adhesive applied to the roof surface. fly in verb2 •To land at an airfield. •To use a flying switch to switch train cars. formsflew in · flown in · flying in · flies in · fly-ins