What is a characteristic of a horizontal sliding window?

A horizontal sliding window is designed with sashes that move side to side within the frame. This characteristic allows for easy operation and ventilation, as one or both sashes can be opened by sliding. Unlike vertical windows, which open by moving up and down, horizontal sliding windows use a smooth tracking system that facilitates easy movement for the glass panes.

The other options describe different types of windows. For example, the first option pertains to windows that open vertically, such as double-hung windows. The second option mentions sashes in upper and lower configurations, which is a feature of double-hung windows rather than horizontal sliders. The third option refers to casement windows, which are hinged and swing open rather than slide. Thus, the defining feature of a horizontal sliding window is accurately captured by its sashes sliding horizontally in the frame.