Learner's definition of OR
1 — used to introduce another choice or possibility
You can have coffee or tea.
Would you like beer, wine, or something else?
He must be her brother—or is he? [=maybe he is not her brother]
I'll call (either) today or tomorrow.
(somewhat informal) I didn't mean to annoy you or anything.
(somewhat informal) Can I get you a cup of coffee or something?
2 — used in negative statements to introduce something else that is also true 3 — used to say what will happen if a specified thing is not done
Finish your dinner or you won't get any dessert. [=if you do not finish your dinner, then you will not get any dessert]
Be at the station by 5 o'clock or you will miss the bus.
4 — used to introduce another number or amount that is possibly the correct one
It's been two or three years since I've seen her.
The package should arrive in five or six days.
We waited for an hour or more.
5 — used to introduce the reason why something said previously is true 6 a — used to introduce a word or phrase that defines or explains what another word or phrase means
b — used to introduce a word or phrase that corrects or states more precisely something you have just said
Botany, or the science of plants, is a fascinating subject. = The science of plants, or botany, is a fascinating subject.
This pan is used for sautéing, or frying, the vegetables.
We got here quickly—or more quickly than last time, anyway. = We got here quickly—or at least more quickly than last time.
The building is 500, or to be precise, 502 years old.
She breeds rabbits, or rather hares.