An envelope is a packaging product, usually made of flat, planar material such as paper or cardboard, designed to contain a flat object such as a letter. The traditional type is 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 when the sides of the sheet are folded about a delineated central rectangular area, a rectangular-faced, usually oblong, enclosure is formed with a symmetrical arrangement of four flap ...
When the folding sequence is such that the last flap to be closed is on a short side it is referred to in the commercial envelope manufacturing industry as a '"pocket"'. Although in principle the flaps can be held in place by securing the topmost flap at a single point (for example with a wax seal), generally they are pasted or gummed together at the overlaps. They are most commonly used for enclosing and sending mail (letters) thr ...
