Inter Area summarisation
area range [area number][prefix] [mask]
A router configuration command used to summarise subnets internally to the OSPF domain between different areas. The area number is the area where the networks are currently received from.
External Summarisation and Redistribution
summary address [prefix][mask]
A router configuration command used to create a summary address for routes learned externally from the OSPF domain.
redistribute [routing protocol or prefix][metric] [metric-type][subnets]
A router configuration command used to redistribute routes learned from another routing protocol, you can assign a metric or metric type depending on the internal protocol (metric-type for OSPF/ISIS or just metric for all internal protocols). The subnets keyword tells OSPF to advertise the network as it is received and not to just advertise the classful network as this is the default.