When I was a little girl I would spend my summers on my grandparent's farm in Arkansas. Each day we would eat breakfast, lunch, dinner, and then supper.
"supper - Any light evening meal, especially one taken late in the evening: an after-the-theater supper."
Supper was usually a tomato sandwich and some blackberries or something similar.
I don't know if this is a southern expression or use of the word. For most Americans supper and dinner mean the same thing. However, Americans rarely use the word, "supper."