What is a Compound Cell?

Hello Good ABD Community

So here is a question I'm asing because I've seen a lot of this "compound cell" topics and tips and tricks and other marvelous features, the only problem is that I don't have a clue of what on earth IS exactly a compound cell.

Probably you must be thiking that every Bentley user must have know this by now, the only problem is that to be honest ABD has like one million (maybe I'm exagerating) diferent features and tips and tricks and stuffs. So please help me here

What is exactly a compound cell? What makes it different from a regular cell?

Regards