I don't know if that's the correct terminology, but I've always seen setups like this:

Main breaker panel outside near the meter. This panel would typically have very few breakers, for example I have one for a garage, one for my home, and a separate one for a 220 outlet.

Then inside my home I have a sub panel that contains additional breakers that turn off specific sections of my home.

So for example one breaker outside can turn off the entire home, then inside many breakers can turn off individual rooms, such as the kitchen, bedroom, bathroom, etc.

On a relatives home I saw recently it only appears to have one panel outside by the meter. I haven't gone through it thoroughly but it has a lot of breakers, similar to what you'd typically see inside.

Any thoughts on that? I was under the impression that you need to have one main breaker that can turn off power to the entire house. I don't know if there is something like that in the one breaker box outside.