Original: We use the following abbreviations: AS = Authentication Server SS = Service Server TGS = Ticket-Granting Server TGT = Ticket-Granting Ticket The client authenticates to the AS once using a long-term shared secret (e.g. a password) and receives a TGT from the AS.
Simplified: Briefly, the client authenticates to AS using a long-term shared secret and receives a ticket from the AS.