A nightie is a type of loose-fitting, sleeveless garment that is typically worn as sleepwear or lounge wear. It can be made from various materials such as cotton, silk, satin, or polyester and comes in different styles including short or long lengths, v-necklines, off the shoulder designs, and more. Nighties are often adorned with cute patterns, lace trims, or embroidery to make them even cozier for sleeping.