SUPPER: 1. A light evening meal when dinner is taken at midday. 2. A light meal eaten before going to bed. DINNER: 1.the main meal of the day, eaten in the evening or at midday. 2.a formal meal in honor of some person or occasion.
Terms: The word dinner comes from the french word diner, which means the chief meal of the day. Dinner can also mean a more sophisticated meal like a banquet. The word comes from the latin disiunare, which means to break fast (like in the english word breakfast). In the United Kingdom and Ireland, supper was originally a light meal eaten just before bedtime. This meaning is still retained for the case of an "after-theatre supper"
It depends on where you are from. The basic rule in my corner of the world is the "big meal" of the day is called dinner and supper is evening meal. Sometimes they are the same, but depending on how you portion out your meals, dinner could be the mid-day meal.