Double-hung windows are a type of window that features two movable sashes, allowing both the top and bottom sections to slide up and down. This design provides flexibility in ventilation, as you can open either sash to let in fresh air while keeping the other closed. These windows are commonly found in residential homes and are popular for their classic appearance and ease of use. They can be made from various materials, including wood, vinyl, and aluminum, making them suitable for different architectural styles and climates.