For us, the midday meal is "lunch" and the evening meal is "supper". "Dinner" is a special meal, usually served on a holiday or celebration day, such as Christmas, Thanksgiving, someone's birthday, or Sunday after church. Lunch is usually lighter than supper; lunch would be something quick to fix: sandwiches, hot dogs, nachos, etc.., while supper would involve more preparation and might even include a dessert. Dinner would be a lot like supper, but much more elaborate, and usually includes fancier foods that we don't get very often.
Here in the Deep South, most people refer to meals this way, except people who have transplanted from elsewhere (they usually say "lunch & dinner") and older people, including my mom (they usually say "dinner & supper").