What is a door mullian?

A door mullion is a vertical or horizontal structural element that divides two or more doors or Windows in a frame, often found in double doors or multi-pane Windows. It serves both aesthetic and functional purposes, providing support and stability to the door system while enhancing the overall design. Mullions can be made from various materials, including wood, metal, or composite materials, and contribute to the security and energy efficiency of the entryway.