The name Kerberos comes from Greek mythology; it is the three-headed dog that guarded the entrance to Hades.

"Cerberus" is the Latin spelling of the Greek "Kerberos", and according to the OED is pronounced like "serberus", but that is quite at odds with the Greek, as the initial consonant is a "k". MIT Project Athena chose to use the Greek spelling and pronunciation.

      Kerberos is a network authentication protocol. It is designed to provide strong authentication for client/server applications by using secret-key cryptography. A free implementation of this protocol is available from the Massachusetts Institute of Technology. Kerberos is available in many commercial products as well.
      Tools to "sniff" passwords off of the network are in common use by systems crackers. Thus, applications which send an unencrypted password over the network are extremely vulnerable. Worse yet, other client/server applications rely on the client program to be "honest" about the identity of the user who is using it. Other applications rely on the client to restrict its activities to those which it is allowed to do, with no other enforcement by the server.
       Kerberos is a solution to your network security problems. It provides the tools of authentication and strong cryptography over the network to help you secure your information systems across your entire enterprise.

Traditional authentication:

CLIENT                                              SERVER

Kerberos:
  Assume hostile network, untrusted client OS
  Strong, mutual authentication
  Institutional scale
  Key distribution to secure app session