What is the difference between broker and broker server?

Please review the documentation for info on this very basic question. You will also find information on the forums and in the glossary.

A Broker host (e.g. a Windows or Solaris server) can run one or more Broker servers, which can manage one or more Brokers.

can anyone provide me with the latest ‘Broker server license key’ required during installation?
i have the older version of keys i guess cse it gives an error invalid key.
thanks in advance