A netmask is the prefix length written as an address: /24 is 255.255.255.0. ANDing an address with the mask gives the network address.
Netmask
A 32-bit mask whose leading ones mark the network part of an IPv4 address.
A netmask is the prefix length written as an address: /24 is 255.255.255.0. ANDing an address with the mask gives the network address.