What's the difference between groups and windows?

I've read the help on what a Group is. To ensure I understand it's functionality -- its purpose is to be at a high level, and under it is one-to-many Windows. If that is correct, I think the confusion in the documentation and in the answer to the question on this thread is that it says "a Group is just a saved window", which makes it sound like the group itself is a window. If I'm understanding it now, it might be better written "A Group is used to collect saved windows." Is that correct, or am I still misunderstanding?

Also confusing is that the "window" icon and "group" icon appear to act exactly the same. You can group windows under windows, and you can group windows under groups. But I'm sure I'm misunderstanding something in the difference in functionality, just now sure what. :-)

Actually any type of node can collect any other nodes inside. And the Ggroup is really just a fancy styled node, with box icon, you can use it for whatever purpose you like. But in case some saved tabs activated inside it then they become an active window.