What does it mean when it says 'room only' in the hotel reservation?

"Room only" means you're paying just for the room, with nothing else included. "Bed and breakfast" (BB) is the opposite: you get the room plus breakfast, so if you see that option it's more expensive but at least you've already got breakfast sorted. The difference is pretty clear, it's mostly so you don't get surprised when you arrive at the hotel expecting free breakfast if you only booked the room.

Room only basically means you pay just to sleep there, nothing else. No breakfast, no meals, nothing like that. You arrive, you have your room, and that's it. If you want to eat something, you have to figure it out on your own, either at the hotel restaurant (paying extra) or going out to find something in the area.

Bed and breakfast is literally the opposite. You get the room plus breakfast included in the price. It's not necessarily a five-star buffet, it depends on the hotel, but at least you have something to start the day without paying extra. Like they mentioned above, the room rate ends up being more expensive, but if you don't want to be searching for where to have breakfast every morning, it's more convenient.

The important difference is the final price. With room only you can save money if you don't mind eating out or if the hotel is in an area with lots of places nearby. With BB you already know exactly what's included and there are no surprises after. When I travel I usually choose based on where the hotel is, honestly. If it's downtown with cafes everywhere, room only; if it's more isolated, I prefer having breakfast guaranteed.

I once booked a hotel in Colombia with "room only" thinking they'd at least give me complimentary coffee and turns out nope, nothing 😅 basically you pay for the room and that's it, if you want breakfast you have to go out and find a café or order room service (which is expensive). With "bed and breakfast" things change because breakfast is included in the price, so you know exactly what to expect and the bill doesn't surprise you at the end. The difference is pretty significant if you're budgeting your trip, because a decent breakfast at a hotel can cost around 15-20 bucks a day.