Any of various types of fold formed by doubling fabric back upon itself and then pressing or stitching into shape WordNet 3.0 & Open English WordNet

A pleat is a type of fold formed by doubling fabric back upon itself and securing it in place. Wikipedia

Deliberate fold in the design of a textile object or garment Wikidata

A flat fold; a doubling, as of cloth; a pleat. OmegaWiki

Flat fold. Wiktionary (translation)

A fold in the fabric of a garment, usually a skirt, as a part of the design of the garment, with the purpose of adding controlled fullness and freedom of movement, or taking up excess fabric. There are many types of pleats, differing in their construction and appearance. Wiktionary

Fold in a fabric of a garment. Wiktionary (translation)