Subnet Mask

Definition: A subnet mask is the IP address-like designation of the size of subnetwork to which a computer or other network device belongs.

For example, the subnet mask of 255.255.255.0 indicates that this subnetwork can contain 256 IP devices.

See more about subnet masks in Bradley Mitchell's Subnet Masks and Subnetting Tutorial.

Examples: "Most home networks are Class C, designated by a subnet mask of 255.255.255.0. This size of network can contain up to 256 IP devices, plenty of room for any normal home or small business!"