I'm also originally from rural Scotland (around Tomintoul), for us it was "Breakfast", "Dinner" and "Supper".
Upon moving to the central belt, and ingratiating myself into more middle class circles of friends I then discovered:
Breakfast - eaten usually when you get up in the morning, say early morning until ~1030am
Lunch - eaten from 12pm until ~2:30pm
Afternoon Tea - taken from around 3:30pm until 4:30pm (cakes/biscuits [cookies] and would also include some kind of sandwich - often cut into triangles)
Tea - 5pm until 6pm - usually a lighter two course meal (say an omlette) and some pudding (desert).
Dinner - taken from 7pm until perhaps 9pm - this would be a fully laiden two or three course meal.
Supper - taken from around 10pm until around 11pm (or just before bedtime) - likely cheese on toast or crackers & cheese and a cuppa.
Obviously you don't need to have every one of these meals every day of the week.
I've heard "Second Breakfast" is actually a thing with farmers, i.e. they get up super early (say 4am) to feed the livestock or do some other such thing (cow milking?) and they have a lightish breakfast - a cuppa, some cereal or maybe toast. Then later on, say 730am-8am, once these tasks are done and dusted, they head back to the farmhouse where they have a more hearty affair - sausages, bacon, eggs.
Damn, forgot about brunch. Too late to edit in now. I left out elevenses because that's really just a cup of tea and a rich tea or digestive. I feel you need a bit more than that for it to be classified as a proper meal.
In spanish I think all countries agree on at least: desayuno (breakfast), comida (lunch), cena (dinner) as the three basic. But we also have merienda and almuerzo which get different times and portions depending on country.
And there can be other terms of course. In Guadalajara, México, where I live, schools say "hora del lonche" (lunch time) to the midday meal.
'Desayuno, comida y cena' is how people refer to the main meals in the Dominican Republic, 'almuerzo' is also used to mean lunch but mostly in formal settings. I also just asked a Colombian friend and he says 'comida' is mostly used to refer to dinner, and 'almuerzo' for lunch.
Edit: He also says 'cena' is a more formal, less common way to refer to dinner.
Lunch is most commonly "almuerzo" in my experience, with some variation. I think there are some Europeans and perhaps pockets of Latin Americans who use "comida" to refer to either lunch or dinner as a meal, while most people use it to refer to food in general. Dinner is "merienda" in some places, while many others reserve the common "cena" for dinner and use "merienda" to refer to an afternoon snack.
'La Comida' as the main meal of the day at approximately lunchtime is a Castillian term and generally a Spanish (in the sense of: people that live in Spain) practice. The practice and this sense of the term 'comida' aren't common in Latin America, in my experience.
Upon moving to the central belt, and ingratiating myself into more middle class circles of friends I then discovered:
Breakfast - eaten usually when you get up in the morning, say early morning until ~1030am
Lunch - eaten from 12pm until ~2:30pm
Afternoon Tea - taken from around 3:30pm until 4:30pm (cakes/biscuits [cookies] and would also include some kind of sandwich - often cut into triangles)
Tea - 5pm until 6pm - usually a lighter two course meal (say an omlette) and some pudding (desert).
Dinner - taken from 7pm until perhaps 9pm - this would be a fully laiden two or three course meal.
Supper - taken from around 10pm until around 11pm (or just before bedtime) - likely cheese on toast or crackers & cheese and a cuppa.
Obviously you don't need to have every one of these meals every day of the week.