An envelope's a packaging product, usually made of flat material such as paper or cardboard, and designed to contain a flat object, which in a postal-service context's usually a letter, card or bills. The traditional type's made from a sheet of paper cut to one of three shapes: the rhombus (also referred to as a lozenge or diamond), the short-arm cross, and the kite. These designs ensure that in the course of envelope manufacture when the sides of the sheet are folded about a delineated central… (More on Envelope)