Definition & Meaning of "door mullion"

What is a "door mullion"?

A door mullion is a vertical or horizontal support piece within a door frame that divides the door into sections. It is commonly found in double or multi-panel doors and serves both functional and decorative purposes. By providing structural support, the mullion helps keep the door stable and maintains its shape. Additionally, it adds visual interest by creating separate sections in the door design. Mullions can be made from various materials, such as wood or metal, and can complement the overall style of the door and the surrounding architecture.