In the United States, this varies a LOT, and not just regionally but on a family-by-family basis.
When I was a kid in my family, we called the meals "breakfast, lunch, and supper," and reserved the word "dinner" for special occasions like Christmas and Thanksgiving. Christmas and Thanksgiving dinners were typically eaten in mid-afternoon, around 2 or 3 pm. We would also used "dinner" for an especially big or fancy meal, perhaps at a restaurant. We would eat "supper" at home by ourselves, but "go out for dinner" or "have someone come for dinner."
My understanding is that on farms and ranches there is a tradition of eating the biggest meal at mid-day. In cities and towns, people who leave home and go to work usually call the meals "breakfast, lunch and supper" or "breakfast, lunch, and dinner."