Original: It makes use of a trusted third party, termed a key distribution center (KDC), which consists of two logically separate parts: an Authentication Server (AS) and a Ticket Granting Server (TGS).
Simplified: It makes use of a trusted third party authentication known as "key distribution center (KDC)", which consists of two logically separate parts: an Authentication Server (AS) and a Ticket Granting Server (TGS).