Hostname

A hostname (occasionally also, a sitename) is the unique name by which a network-attached device (which could consist of a computer, file server, network storage device, fax machine, copier, cable modem, etc.) is known on a network.

DreamHost
In DreamHost parlance, a hostname usually refers to the subdomain that references a MySQL database; however, the word can also refer to any domain name or subdomain name.