flap seat noun2 •A hinged seat that can be raised when not in use.The taxi got too tight. Ray’s knees jammed sideways by Leopold’s suitcase, which had been moved to let down the flap seat, bulked between the children — 1935 •A flap on the part of an undergarment or night garment that covers the buttocks.After several minutes, Liebknecht stood barefoot in a suit of long winter underwear. Some of its buttons were missing and the flap seat was baggy from too much laundering. — 1954 formsflap seats
