dongle

A small hardware device that dangles from a cable that plugs into a port to add some sort of capability. In asymmetric digital subscriber line (ADSL) installations, for example, the customer generally is provided with a number of dongles that are microfilters that plug into telephone sets or fax machines that share the ADSL line. The filters prevent the telephones and fax machines from causing interference between the analog voice channel and the digital data channel when they go off hook or on hook, or when the telephone or fax receives a ringing signal. Dongles often are used for smart cards and other security devices that provide copyright protection for very expensive software programs or that protect access to virtual private networks (VPNs). See also ADSL, cable, channel, hardware, interference, microfilter, port, software, and VPN.