On a window the apron is the molding or trim that’s set under the stool or sill. It is employed as a both a decorative and practical characteristic. Like the casing, it insures in which the window’s frame along with the wall covering meet.
Aprons not only include detail, but hide the gap between the wall covering and the frame of the window.
Metropolitan Window Company
This apron is constructed up and extends below the base of the window.
Christian Gladu Style
Aprons include a finished look even to little windows.