Hey, Grandpa, what’s for supper?
I grew up in the midwest with one midwestern parent and one Appalachian one. We called the evening meal supper. As an adult, I live in the midsouth. In urban areas, it’s mostly dinner. Once you leave the city, you’ll hear supper more often.
IME, the divide is more rural vs. urban rather than what part of the country.
This is the traditional pattern where I come from. Boarding schools, the army and the folks who can afford it, like myself, still follow it. I would hate my belly to bulge with food when I’m supposed to relax and I don’t see the point of a substantial meal after 6 or 7 o’clock either.
It does come from the drink tea, yes. There’s all sorts of fascinating social history associated with it, if you’re interested in that sort of thing, but it generally just means a (usually) light meal in the late afternoon. Depending on your definition of “light”, of course – like dinner, it’s something that some people have tended to define by the time of day, rather than what it consists of.
It’s breakfast, lunch, and dinner at Casa Doorhinge.
Of course, breakfast (food) can be eaten at all three meals. 
I call it “Darryl”.
Breakfast, lunch and supper are my usual meal words. “Dinner” is a fancier version of supper (e.g. at a nice restaurant or in phrases like “dinner party”).
Dinner - largest meal of the day. Usually in the evening, but can be midday on holidays or Sunday.
Supper- a smaller evening meal, eaten either when dinner was at midday or after seeing a movie or a concert etc.
Dinner - largest meal of the day. Usually in the evening, but can be midday on holidays or Sunday.
Supper- a smaller evening meal, eaten either when dinner was at midday or after seeing a movie or a concert etc.
Jesus Christ! Why didn’t I think of that? 
The word dinner isn’t part of my vocabulary at all. We have:
Breakfast
Brunch
Lunch
Supper.
No dinner.
ETA: Breakfast and brunch need not be on the same day.
I said supper because that’s what it was called in my house when I was growing up*. If I go out for an evening meal at a restaurant or someone else’s house, that’s dinner.
*and my mom would sing “OH it’s suppertime, yes, it’s supper time, the very best time of day!” accompanied by a small dance.
Breakfast or tiffin in the morning, lunch at noon, dinner at night. Lots of Indians have a more substantial meal in the morning and evening/night, usually called tiffin. When it’s a light meal, I just call it an (evening) snack.
In Tamil, my mother tongue, all meals are called just that, “meal”. When a distinction is needed, you could say morning meal etc, but it’s usually needed in everyday conversations.
For my family, it’s always been “supper,” in the everyday casual sense. Except a holiday meal, or when going out to a dressy function, in which case it’s “dinner.” You wouldn’t say “Thanksgiving supper.”
Dinner, but dinner is also a holiday meal at any time. My great-grandmother served Thanksgiving and Christmas dinners at something ridiculously early like 10:30 or 11:00, and that was dinner.
When do they eat lunch?
She DID tell you what that was all about, right?
Breakfast
2nd breakfast
Elevenses
Luncheon
Afternoon tea
Dinner
Supper
Speaking as a city slicker, “Dinner” is the large meal brought out course by course into the Dining Room by the servants at 8PM, for which I am wearing white tie.
“Supper” is the hot bird and cold bottle enjoyed after eleven, often in the company of another “hot bird.”
How pleasant it is to have money, heigh ho!
How pleasant it is to have money!
Tea. But everyone around me calls it dinner.
I think it was a Snoopy dance? 
She also did a wonderful goonie bird impression.