olemus
(1) bittmask võrguosa väljaeraldamiseks IP-aadressist,
sealhulgas alamvõrgumask
= bitmask to extract the network part from the IP address, e.g. the subnet mask
http://unixwiz.net/techtips/netmask-ref.html

http://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html

http://www.zytrax.com/tech/protocols/ip-classes.html

(2) klassi määrav bittmask klassadresseerimisel
= class-defining bitmask in class addressing
https://en.wikipedia.org/wiki/Classful_network