An AS is a group of routers that share similar routing policies and operate within a single administrative domain.
After the initial exchange, incremental updates are sent as network information changes. Incremental updates are more efficient than complete table updates.
When two routers establish a TCP enabled BGP connection, they are called neighbors or peers.
IGP: A routing protocol that exchanges routing information within an autonomous system. EGP: A routing protocol that exchanges routing information between different autonomous systems.
RIP, IGRP, OSPF, IS-IS, and EIGRP are examples of IGPs. BGP is an example of an EGP.