container vs. group in REST API


I apologize is this is obviously documented somewhere. If so I had trouble finding it.

What is the difference between containers and groups?

At least in the cases I have looked at, containers seem to have the same names as groups so I don't understand the difference.

Also, there is no containers entry in the REST API documentation. It would be nice to get a list of all containers, similar to how you can get a list of all groups.

Thank you for any information.