What does route summarization mean?

Summarization is the process by which we collapse many routes with a long mask to form another route with a shorter mask. Refer to OSPF and Cisco Route Summarization and the “Summarization” section of Enhanced Interior Gateway Routing Protocol for more information. The auto-summary command works only if you have contiguous subnets. If you work with discontiguous subnets, you need to use the ip summary-address interface configuration command on every interface that participates in the routing process where you want to configure summarization.