A double-hung window is a type of window that has two movable sashes (the part of the window that holds the glass) that slide up and down within the frame. 

This design allows you to open either the top sash, the bottom sash, or both, providing good ventilation options. Double-hung windows are popular for their ease of use and classic appearance, and they often feature tilt-in sashes for easier cleaning. They are commonly used in both traditional and modern architecture.

 If you have specific questions about their operation, installation, or maintenance, feel free to ask!