A pleat is a type of fold formed by doubling fabric back upon itself and securing it in place. It is commonly used in clothing and upholstery to gather a wide piece of fabric to a narrower circumference.
Pleats are categorized as pressed, that is, ironed or otherwise heat-set into a sharp crease, or unpressed, falling in soft rounded folds. Pleats may also be partially sewn flat and allowed to fall open below.
Small pleats sewn in place down their entire length are called tucks.