Depends on the situation. Dinner is your biggest meal of the day. If you have a large, traditional lunch-time meal, it is dinner and your smaller evening meal is supper. If you have a modest midday food-fest, it is called lunch, followed by your larger evening dinner. I guess if neither is particularly substantial, it would be lunch and supper with no dinner, or I guess if you are a rather fat and greedy bastard you could enjoy two dinners in one day.