Pleats are a fold or doubling of fabric that is pressed, ironed or creased into place. (Pleats that are sewn into place are called tucks). There are many varieties, but the side and box pleat are the most common, although they can be accordion, cartridge, circular, curtain, draped, fluted, Fortuny or French. They can be inserte, as well as inverted. Pleats add an even greater fullness to a shape (particularly the skirt). Think Marilyn Monroe over the air vent in ‘The 7 Year Itch’.