Thanks for all the replies and suggestions so far. Yes, Terry, it can be a screen door, but it can also be a door with glass, which is what I have.
Here is a link to some images of storm doors:
https://www.lowes.com/c/Storm-doors-frames-Doors-Windows-doo...Wikipedia says there are three basic types of storm doors: Full-View, Retractable Screen, and Ventilating.
Full-View storm doors[1] typically include a full glass panel and most an interchangeable full screen.
Retractable Screen storm doors feature a screen that is rolled up into the frame of the storm door when not in use.
Ventilating storm doors generally include a full or half screen that is always in position on the storm door.
https://en.wikipedia.org/wiki/Storm_door