This is almost an impossible question to answer definitively, because English-speaking people have different names for meals, depending on where they live, on their age, their class, their background, and family traditions. Even within Britain, the only name for a meal which we can all agree on is breakfast! So, this isn't a definitive answer, but it's one that some people will agree with, at least in the UK. Dinner is the main meal of the day, usually consisting of two or three courses. It is usually the evening meal, but it can also refer to a daytime meal. Christmas dinner, for example, is eaten in the middle of the day, but it is called 'dinner' because it's a large, and relatively formal meal. Supper is always an evening meal, but the word 'supper' suggests something lighter and more modest than 'dinner'. So if your friend invites you for 'dinner' in the evening, this might be quite a large, carefully prepared meal of three courses. But if they say 'Let's have some supper', it might be something more casual, such as a bowl of pasta. Supper is also usually eaten relatively late (by British standards). For example, if you come home late after a concert or show, you might have a light supper afterwards, rather than a large meal.

I've been living in the US my entire life and I've never figured out the difference between dinner and supper. I have never even met someone who actually differentiated between the two. Over the years, I've encountered people who call dinner "supper" and people who call dinner "dinner". Either way, you are still eating the last meal of the day regardless of what you call it. As such, for me, by de facto, they are both one and the same.

Hah! This is a question that puzzles people in the United States and leads to occasional misunderstandings. The names used tend to vary from family to family. As far as I know, "supper" is always in the evening, perhaps 6 p.m. to 8 p.m. "Lunch" is always in the middle of the day, around noon. "Dinner" can be at any time, and is usually the big meal of the day. Commonly, but not always, the evening meal is the big meal. Some families would speak of "breakfast, lunch, and supper" while others would speak of "breakfast, lunch, and dinner." Regardless of custom on ordinary days, a seasonal, big family get-together featuring a huge meal would often be called "dinner"--"Thanksgiving dinner," "Christmas dinner"--which could be at absolutely any time. My family usually ate "lunch" around noon and "supper" around 6, but "Thanksgiving dinner" was eaten around the middle of the afternoon, 2 or 3 p.m.

I've never heard "supper" referred to as a snack but only as the main evening meal, as an alternative word for dinner".

These two words vary a lot by region, 'supper' in particular. Every time this question comes up, I feel like every person has different answer even if they're from the same country! To me, dinner is the last big meal of the day while supper is a very formal dinner ex. a company might have a company supper once a year, which is a formal dinner organised by the company for its employees.