key - A unique value (digital signature) associated with a specific user on a network for the purposes of network security. See also digital key.

keyed - A jack, outlet, or connector is considered keyed when it requires a specific orientation.

keying - The mechanical feature of a connector system that guarantees correct orientation of a connection, or prevents the connection to a jack, or to an optical fiber adapter of the same type intended for another purpose. (TIA)

keypad - An alphanumeric grid that allows a user to enter a personal identification code.

key service unit (KSU) - An electromechanical telephone main control unit where telephones have multiple buttons permitting the user to manually select outgoing or incoming central office telephone lines. It is not necessary to dial an access code for an outgoing line.

key system - See key service unit (KSU).

key telephone system (KTS) - Terminals and equipment in a local environment that provide immediate access from all terminals to a variety of telephone services without attendant assistance.

key telephone system (KTS) ground terminal - A screw terminal located on the key system power supply that must be connected to the grounding lug on the station protector.

k-factor - In tropospheric radio propagation, the ratio of the effective Earth radius to the actual Earth radius. The k-factor is approximately 4:3.

known user - Users with pre-established identities on a network. Contrast with unknown user.