A "double-hung" window is 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 users can open either sash to control airflow. Double-hung windows are commonly found in residential buildings and are popular for their classic appearance and ease of use. They can be made from various materials, including wood, vinyl, and aluminum, and are often chosen for their energy efficiency and aesthetic appeal in homes and buildings.