4.1.2. Prefix and Network Mask

The prefix (CIDR notation) or network mask defines which portion of the address is the network vs host.

172.16.0.0/16    means    172.16.0.0 with mask 255.255.0.0
192.168.1.0/24   means    192.168.1.0 with mask 255.255.255.0
10.1.1.0/30      means    10.1.1.0 with mask 255.255.255.252

Reading it in show ip route: routes are grouped under their classful network, and a header such as 10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks means the subnets listed beneath it use different prefix lengths (VLSM). A connected /24 plus its /32 local (L) route is already enough to trigger it.