network mask

Specifies which are the subnetwork and host parts of an IP address. Also known as a subnet mask, netmask or address mask, the network mask is used to specify which parts of the dotted quad of an IP address identify the subnetwork the host is on and which parts identify the host itself. Network masks are usually represented in either dotted quad notation (for example, 255.255.255.0) or CIDR notation (for example, 192.0.2.0/24).