a book (or manuscript) consisting of large sheets of paper folded in the middle to make two leaves or four pages; "the first folio of Shakespeare's plays"
a mechanism consisting of a metal honeycomb through which hot fluids circulate; heat is transferred from the fluid through the honeycomb to the airstream that is created either by the motion of the vehicle or by a fan
heater consisting of a series of pipes for circulating steam or hot water to heat rooms or buildings