Definition & Meaning of "window mullion"

What is a "window mullion"?

A window mullion is the vertical or horizontal bar that divides a window into smaller sections or panes. It provides structural support to the window and can also add a decorative element by breaking up large expanses of glass. Mullions are commonly made from materials like wood, metal, or plastic, depending on the style and purpose of the window. They help enhance the appearance of the window while maintaining stability and strength, and are often used in windows with multiple panels to create a more detailed or traditional look.