What is a combination safe?

A combination safe is a receptacle which has a lock that is not opened by a key but by turning a dial to a set of numbers in appropriate sequence which will then cause the lock to open. The major benefit is that it is more secure than a receptacle which can be opened with a key. A key can be stolen and used by anyone. But you have to know the combination to open that kind of safe.

BTW, when I say 'receptacle', it can be a small thing like a portable cabinet, or it can be a large room in a bank with a heavy door that opens only in response to the right combination.