- noun a pattern of binary data bits that is used to block out parts of an address data word. It is normally used to separate the network and subnet parts of an address within a long Internet or IP address.
- A bit combination which identifies which portion of an IP address corresponds to the network or subnetwork, and blocks out the rest. For example, a network may use the same values in the first three address fields of a four field address such as WWW.XXX.YYY.ZZZ, and block out, or mask, all but the ZZZ portion, since it is the only one that will vary. Also called subnetwork mask.