A "single-hung" window is a type of vertical sliding window that features two sashes, but only one of them is operable. The bottom sash can be raised to open the window, while the top sash remains fixed in place. This design allows for ventilation while maintaining a clear view through the upper portion of the window. Single-hung windows are commonly used in residential buildings due to their simplicity and cost-effectiveness. They are easy to operate and can be found in various styles and materials, making them a popular choice for homeowners looking to enhance their home's aesthetics and functionality.