BGP speakers peer with other routers to form a vast system of over 60,000 ASNs to comprise the internet. No one router could handle that volume of traffic alone, so neighbor (peering) relationships are important.
There are two types of peer relationships:
IBGP: Run between BGP speakers within the same autonomous system. To avoid loops, one IBGP router will not forward routes learned from another IBGP session (this is called BGP split-horizon).
EBGP: Run between BGP speakers that reside in different autonomous systems. These ASNs typically have different routing policies between them.
Stuck-in-Active: Journal of an IT-Network Administrator 