A job title or role.

A NetworkAdministrator adminsters a network, which usually an IntraNet and a connection to the InterNet. This typically includes both the physical hardware and network-oriented software (DNS servers, WebProxies, etc). It may also include servers for mail, files (Samba, NFS, etc), WebServers (IIS/Apache for FTP, HTTP, etc) and so forth.

See also: SystemsEngineer and SystemAdministrator (and KnowYourSysadmin)