client
     an entity that can obtain a ticket.  This entity is usually either a user or a host.

host
     a computer that can be accessed over a network.

Kerberos
     in Greek mythology, the three-headed dog that guards the entrance to the underworld.  In the computing world, Kerberos is a network security package that was developed at MIT.

KDC
     Key Distribution Center.  A machine that issues Kerberos tickets.

keytab
     a key table file containing one or more keys.  A host or service uses a keytab file in much the same way as a user uses his/her password.

principal
     a string that names a specific entity to which a set of credentials may be assigned.  It can have an arbitrary number of components, but generally has three:

     primary
          the first part of a Kerberos principal.  In the case of a user, it is the username.  In the case of a service, it is the name of the service.

     instance
          the second part of a Kerberos principal.  It gives information that qualifies the primary.  The instance may be null.  In the case of a user, the instance is often used to describe the intended use of the corresponding credentials.  In the case of a host, the instance is the fully qualified hostname.

     realm
          the logical network served by a single Kerberos database and a set of Key Distribution Centers.  By convention, realm names are generally all uppercase letters, to differentiate the realm from the internet domain.

     The typical format of a typical Kerberos principal is primary/instance@REALM.

service
     any program or computer you access over a network.  Examples of services include ``host'' (a host, e.g., when you use telnet and rsh), ``ftp'' (FTP), ``krbtgt'' (authentication; cf. ticket-granting ticket), and ``pop'' (email).

ticket
     a temporary set of electronic credentials that verify the identity of a client for a particular service.

TGT
     Ticket-Granting Ticket.  A special Kerberos ticket that permits the client to obtain additional Kerberos tickets within the same Kerberos realm.