Definition of "ruching"

Mantillas are larger than last year, and are generally all worn with a deep flouncing, either of the same material, or of black lace; the mantilla itself is also much trimmed with small ruchings of ribbon, guip and guipure lace, laid on quite flat.

1855, “Mantillas and Shawls”, in Graham's American Monthly Magazine of Literature, Art, and Fashion, volume XLVI, number 4, Philadelphia, Pa.: Abraham H. See, 106 Chestnut Street, page 578

Probably for the first time since Lindsay Lohan was born, fashion designers, from the high-end likes of Miuccia Prada and Stella McCartney to mainstream classics like Jantzen, have taken a more refined approach to swimwear, emphasizing one-piece looks, halter tops, high-waist boy shorts and ruffles and ruching as camouflaging details.

2008 May 15, Eric Wilson, “Out with Vegas, in with vamp”, in The New York Times‎