Breakfast, lunch, dinner or supper. Dinner is a bigger meal, supper is smaller, more casual...could be grilled cheese and soup, or a chef salad, etc. Dinner is a meat, at least two vegetables, and probably a salad and bread. My parents used to have Dinner at noon on Sundays, weekdays it was usually supper.
Dinner is, traditionally, the largest meal of the day, while supper is the last meal of the day. For some, the mid-day meal is the larger meal of the day and so you may find these are the people who refer to luncheon as dinner. Supper would then be a smaller, later meal.
I refer to the meals as breakfast, lunch and dinner, but often say supper as well.
Out on my grandparents (both sets) farm, it was dinner (noon meal--largest of the day) and supper (light evening meal), so we had the same names at my house in town. However, supper was always the bigger meal here. Mom said that on the farm the noon meal was bigger to give the men fuel.
In my ex's family it was lunch (light) and dinner. . . .
Over the years things have gotten mixed up and who knows what i call it from day to day. I generally use lunch for the noon meal and supper for the evening meal, so I'm a hybrid LOL.