Nightwear, also called "sleepwear", "nightclothes", or "nightdress", is clothing designed to be worn while sleeping. It is generally worn otherwise only in the company of those one knows well. Some nightwear usage is seasonal, i.e. some persons only wear nightwear in winter.
A Nightgown (also called a nightdress) is a loosely hanging item of nightwear nowadays solely for women. Its length may vary from hip-length (babydoll) to floor-length (peignoir) but is typically knee-length. A nightgown is manufactured of e.g. cotton, silk, satin, or nylon. It may be decorated with lace appliquιs or embroidery at cups and hem. A short nightgown is often called nightie.
Pajamas or pyjamas (often PJs) are a form of nightwear that are usually two-piece garments but may be one-piece garments.