Supernetting/CIDR are used to denote a range of ip addresses. For example 172.20.0.0/16 equals 172.20.0.0-172.20.255.255. Usuually used by ISPs to route large IP ranges (BGP, eBGP..etc) and are used to distribute IP ranges to owners, as in from ARIN, the people who manage public IP addresses for the US.
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what is super netting