4.1 OSPF Overview
4.1.2 OSPF terminology
It is important to understand the unique terms associated with OSPF and link-state routing in general. The following list introduces the various terms that will be used in this chapter and that are shown in the figures.

Link --- A physical and electrical connection between two network devices. 
Link-state --- The status of a link between two routers. This status includes information about a router's interface and its relationship to neighboring routers.
Cost --- The value assigned to a link. Rather than hops, link-state protocols assign a cost to a link, which is based on the speed of the network connection.
Area --- A collection of networks and routers that has the same area identification. Each router within an area has the same link-state information. A router within an area is called an internal router.
Designated Router (DR)) --- One router on an OSPF multiaccess network that is elected to represent all the routers in that network. Each OSPF network has a DR and BDR. These routers have special responsibilities that are discussed later in this chapter.
Backup Designated Router (BDR) --- A standby router that becomes the DR, if the original DR fails.
Adjacencies database --- A listing of all the neighbors to which a router has established bi-directional communication.
Link-state database (or topological database) --- A list of information about all other routers in the network. It shows the network topology. All routers within an area have identical link-state databases.
Routing table --- The routing table (also known as the forwarding database) is generated when an algorithm is run on the link-state database. Each router's routing table is unique and contains information of how and where to send packets to other routers.