Noun
hostmask (plural hostmasks)
(Internet) On IRC, a partial address that matches a number of hosts.
The channel operator banned the hostmask *!*@*example.com, so nobody could connect from example.com any more.
The format of a hostmask is nick! Source: Internet
Users may also have the option of requesting a "virtual host" (or "vhost"), to be displayed in the hostmask to allow further anonymity. Source: Internet