OSPF supports multi-process. This allows multiple OSPF processes to run independently on the same router. Route exchanges between different OSPF processes are similar to route exchanges between different routing protocols.
Each router interface belongs to only one OSPF process.
OSPF multi-process typically applies to the scenario where OSPF runs between provider edges (PEs) and customer edges (CEs) in a VPN whereas OSPF is used as an IGP on the backbone of the VPN. On the PEs, the two OSPF processes do not affect each other.