My little sister ask me this question, and i am here to seek answers.

In parts of the US, supper and dinner are used interchangeably to refer to the evening meal, but elsewhere dinner is the midday meal, akin to lunch , and supper, the evening meal. What do these words really mean?
The word dinner does not necessarily imply the time of day. Depending on where you are, it may mean the midday meal or the evening meal, but it always refers to the main meal of the day. The word dinner comes from the Vulgar Latin word disjējūnāre meaning “to break one’s fast.”
Supper , on the other hand, is associated with the evening. It comes from the Old French word souper meaning “evening meal.” It has traditionally been used in the context of the last meal taken by Jesus before his crucifixion, known as the Last Supper.
So if someone asks you over for dinner, how do you know what time they expect you? That may depend on where you are. In 1828, Noah Webster wrote that “The dinner of fashionable people would be the supper of rustics,” reflecting the prominence of dinner as the term for a midday meal in some rural parts of the country. Regardless of time of day, if you are going over for dinner, you can expect a feast.
More recent data from Google Ngram suggest that use of the word supper has been declining since the beginning of the 1900s, while the use of lunch has been increasing.
Dinner holds the top spot on the lexical food chain as the most widely used term of the three. Which term do you use most often?

They are kinda similar. The only difference is that supper always comes last before going to bed.