I’ve seen cases where a noon-time meal is referred to as dinner, and the evening meal is called supper. There’s also lunch around noon followed by dinner in the evening. Is there a particular difference between dinner and supper, or a circumstance where lunch becomes dinner?
Dinner is considered to be the “main” or largest meal of the day. Whether it takes place at noon or in the evening is mostly a cultural thing. For instance, many people who grew up in the American South and/or on farms traditionally ate larger meals at noontime to give them the strength to keep working through the afternoon.
Supper is more specifically a lighter evening meal. Rooted in the word “to sup”, it comes, again, from farming traditions — many farming families would have a pot of soup cooking throughout the day, and would eat it in the evening — specifically, they would “sup” the soup.
Lunch is almost the midday equivalent of supper — it’s also a lighter and less formal meal than Dinner, but is used specifically when referring to a midday meal. So whether you use lunch/dinner or dinner/supper is heavily determined by when your culture traditionally has its largest meal.
Much Later Edit: I happened across this article discussing the agricultural roots of midday dinner and evening supper, just to add a bit more to the conversation.