glass curtains

Thin, flat-hanging curtains fitted against the glass of a window or door, or immediately over a shade, and usually kept drawn over the glass to soften the light and give privacy. For thin, often sheer curtains used under the main curtains to soften light, use "undercurtains." For curtains made of any transparent or very lightweight material, often plain white and often used as undercurtains, use "sheer curtains."