What is a "blackout (curtain)"?

A blackout curtain, also known as a room darkening curtain, is a type of window treatment that is designed to block out sunlight and provide complete privacy. Blackout curtains are typically made of thick, opaque materials such as polyester or velvet, and are designed to fit snugly against the window to prevent light from entering the room. They can be used in bedrooms, nurseries, and other spaces where complete darkness is desired, and can also be used to reduce noise and improve energy efficiency. Blackout curtains come in a variety of styles, colors, and patterns, and can be easily customized to fit any window size or shape. They are a popular choice for those looking to create a cozy and comfortable atmosphere in their home, and are an effective way to control the amount of light and privacy in a room.