The mechanism that opens and closes the phone line to a phone. It is typically located at the top of the phone's base (and therefore beneath the phone's receiver) and is released by the act of removing the handset from the cradle, hence the term "off-hook." Host 1) A computer system that provides service features to other computers. Used in this context, any computer that acts as a server can be considered a host, whether on the Internet or a Local Area Network (LAN). 2) The provision of a computer to house a web server for one or several web sites.