Breakfast is always breakfast.
The midday meal is 'lunch' if you live in the South. 'Luncheon' if you are posh, wherever you live. If you live in the North, it's 'dinner'.
The main meal of the day is 'dinner' if you live in the South, 'supper' if you are posh. 'Tea', if you live in the North. Northerners may also have a snack before going to bed, and this is called 'supper' I don't know if Southerners or posh people have an equivalent.
Aspirational middle-class folk will always use the Southern terminology, no matter where they live. Oh, there's also 'afternoon tea' but I'm not sure how that fits into anything. And 'elevenses', but I don't call a cup of tea and a biscuit a meal.
What's brought this on? I can hear you asking. Well, BetterArf is now back at work and yesterday invited one of her colleagues round for tea. 'Hell no, I'm not coming for tea! I'm an American, I drink coffee!"
I kid you not.