Subnetwork

Netmasks (or subnet masks) are a shorthand for referring to ranges of consecutive IP addresses in the Internet Protocol. They used for defining networking rules in e.g. routers and firewalls.

A netmask is a shorthand for describing a range of IP addresses. A netmask may describe just a single IP address:

192.168.0.1/32: just the address 192.168.0.1

Or all possible IP addresses:

192.168.0.1/0: all 4.3 billion addresses from 0.0.0.0 to 255.255.255.255

More usefully, it does something in between:

192.168.0.1/31: the IP addresses 192.168.0.0 and 192.168.0.1

p.s. happy new year!