In OSPF, it's called "Area". All OSPF networks have at least one area with the default being area 0. If more than one area exists, area 0 is defined as the backbone area and is used to connect all other areas.
I think the OP might be referring to the process ID:
[code:1]Router(config)# router ospf 123[/code:1]
In this example, the OSPF process ID is 123; this number is only locally significant. The process ID is used to distinguish between different OSPF processes on the rare occasion you need to run more than one.
This is in contrast to, for example, EIGRP, which communicates an actual AS number to its neighbors.