Classless Inter-Domain Routing as method of specifying a range of IP Addresses.
It comprises an IP address and a routing prefix. The routing prefix defines how many of the 32 bits in the IP address are fixed (the flexible bits make up the IP addresses in the range)
e.g. 192.0.2.0/24 has 24 fixed bits: 192.0.2, therefore the range is 192.0.2.0 - 192.0.2.255.