Meals
There are regional and social differences in the names for meals.
British usage
Midday: dinner or lunch
The midday meal is often called dinner, especially if it is the main meal of the day. People who are ‘higher’ in the social scale usually call it lunch. Lunch is also the normal term used by most people for a light midday snack or packed meal.
Afternoon: tea
(Afternoon) tea (a light meal of tea with biscuits and cakes, taken at four or five o’clock in the afternoon) is now very unusual, though it is often served in hotels.
Early evening: sometimes (high) tea or supper
Many people have a cooked meal around five or six o’clock. This is often called tea or high tea; some people call it supper.
Later evening: supper or dinner
A meal later in the evening is often called supper (and some people use the same word for a bedtime snack). Some people use dinner for the evening meal if it is the main meal of the day. A more formal evening meal with guests, or in a restaurant, is usually called dinner.
American usage
Americans generally use lunch for the midday meal and dinner or supper for the evening meal. Celebration meals at Christmas and Thanksgiving are called Christmas/Thanksgiving dinner, even if they are eaten at midday.