bi-fold door(n = noun.artifact) - an interior door;
is a kind of interior door
has parts: flexible joint, hinge

accordion door, back door, barn door, car door, cargo door, door, door guard, door latch, door prize, double door, dutch door, exterior door, fire door, folding door, french door, front door, half door, hatchback door, interior door, louvered door, next door, open door, outside door, revolving door, screen door, service door, show the door, side door, sliding door, stage door, storm door, swing door, swinging door, trap door, wicket door