CIDR notation is a syntax of specifying IP addresses and their associated routing prefix. It appends to the address a slash character and the decimal number of leading bits of the routing prefix, e.g., 192.168.2.0/24 for IPv4, and 2001:db8::/32 for IPv6.
Read more about CIDR Notation: Background, CIDR Notation, Subnet Masks, CIDR Blocks, Prefix Aggregation, See Also