CIDR notation is a compact representation of IP address blocks that consists of an IP address and a suffix that represents number of bits for the network address.

Example: the IPv4 block 192.168.100.0/22 represents the 1024 IPv4 addresses from 192.168.100.0 to 192.168.103.255, because the equivalent of 192.168.100.0 is 11000000.10101000.01100100.00000000 where the bold part is the prefix and rest of the bits represent host addresses. So, the last address here would be, 11000000.10101000.01100111.11111111 which is 192.168.103.255.