Moved from Chicago to central Illinois back when I was a kid. It confused the heck out of me when people called lunch - ‘dinner’.
I call it The Hour of Shame.
In our family, the evening meal has always been dinner. Supper is a light meal you might have after an evening event. For example, if we went to a concert or a play and stopped for something to eat afterwards, that would be supper.
I voted for dinner and supper and it seemed to accept both votes.
On the farm it went this way:
Breakfast - huge meal to start the day
Dinner - Big meal at about mid-day
Supper - light meal in the evening
Lunch - word used by city folk who didn’t know any better
I just remembered a girl I used to work with who was from rural Ma. and used to say supper. My vague memory has her telling me something about if anyone used the word “dinner” at her house her father would mock them and say "Dinner? Who are we eating with, the Kennedys? " 
Grew up and lived my whole life in the suburbs of Chicago. Growing up, we always called it “supper.” Somewhere along the line I started calling it “dinner.” No, I don’t know why.
Dinner if its the biggest meal; supper if it isn’t.
If the biggest meal happens around noon it is dinner and not lunch. Lunches are always small and pretty light.
This is one of the first disagreements my wife and I had after we got married. Having grown up in the suburbs, I considered the two equivalent as meaning the evening. My wife, who has tons of aunts and uncles who are farmers, argued that dinner was the biggest meal of the day, no matter what time. Farmers, she explained, would usually have a big dinner earlier in the day, as a break from working in the fields, and then a smaller supper later in the evening.
Or, what Doctor Jackson said.
Dinner and supper both mean “the evening meal” to me, though I really never use the word “supper” myself.
I grew up in the Midwest (Wisconsin and Illinois); both of my parents were from Wisconsin, as were their parents. Even so, my maternal grandparents used “dinner” to refer to the noon meal, which confused the heck out of me when I was a kid. Despite this, my mother always called the noon meal “lunch”, at least by the time I was around. 
The Last Supper
Growing up in New England it was always supper. When I moved away I started calling it dinner, because everyone else did and it wasn’t worth the fight. You’ll never take “soda” away from me though, “pop” people. Never!
When I was growing up in the Bronx, the evening meal on weekdays, which was the largest of the day, was supper. The smaller mid-day meal was lunch.
We would have a large meal earlier in the day on Sundays, in the early afternoon, and this was Sunday dinner. We would still have a smaller supper in the evening. As Catholics we were supposed to fast before receiving communion at Mass in the morning, so that we wouldn’t have breakfast - usually fresh rolls and pastries from the bake shop, rather than cereal as on weekdays - until after Mass.
Wherever else I’ve lived in the US the evening meal has been dinner, and supper was almost never used.
When I lived in New Zealand it took some getting used to meals being referred to as “tea.” I was especially confused when a friend told me he “had to give the dog his tea.” "These people even serve tea to dogs!,: I thought. 
I call it “dinner,” for sure. Growing up out West I’ve always felt that “supper” was a term used either A) down South or B) more commonly back a few decades. (Although I think my wife uses the term “supper” on occasion and she’s from the Midwest, originally, and she’s not that old [yet] - 
)
Dinner gets used for lunch a lot in my experience of the Midwest. Not just by older ones, either. Never heard it used that way in my years in CA, CO, or TX. Ymmv, of course.
As I grew up, we had breakfast, lunch, dinner. Supper could be used to mean dinner, but if going out, dinner is always called dinner.
Now I have coffee, breakfast, lunch, break, dinner, snack. Not all each day. You would think I should weigh more, but I don’t.
Can someone explain ‘Tea’? I can understand it being used as a teatime, traditionally 4pm boost of tea and some snack, usually well before Dinner/Supper. But one other posted indicated that it may be used for a full meal? Does Tea in such a use have anything to do with the drink tea? Perhaps the letter ‘T’ meaning table or something?
Dinner if it’s the biggest meal of the day. Supper otherwise.
A suburbanite through and through, I am yet not completely divorced from farm culture, in which dinner often happens midday.
This is exactly what my dad tells me.
My mom and step-dad call the noon meal “lunch” every day but Sunday; then it’s called “dinner.” And the evening meal is “supper.”
For me:
Breakfast
Lunch
Dinnner
Supper’s Ready!
This post explains exactly why I am a lurker - someone will be along to say it better and more succinclty than I could. Cross out ‘Bronx’ and write in ‘Baltimore’, and forget the New Zealand stuff, and you have me.