Which window type is characterized by having one sash that can be operated while the other remains fixed?

The single hung window is accurately characterized by having a design where one sash, typically the lower one, can be opened and closed while the upper sash remains fixed in place. This type of window allows for ventilation through the movable lower sash, making it a practical choice for many residential applications.

In contrast, a double hung window features two operable sashes, allowing both the upper and lower sashes to move independently. Sliding windows operate by horizontally shifting one or more sashes to allow for ventilation, while casement windows are hinged on one side and swing open outward, providing a different functionality. Each of these alternatives differs significantly in operation and design compared to a single hung window, reinforcing why the latter's defining characteristic is the fixed upper sash paired with an operable lower sash.