A telephone operated by means of buttons on a keypad and connected to several telephone lines to form an interconnected system, typically in a business or other organization; originally and frequently attributive, especially in "key telephone system".
Origin
1950s.
Definition of key telephone in US English:
key telephone
noun
A telephone operated by means of buttons on a keypad and connected to several telephone lines to form an interconnected system, typically in a business or other organization; originally and frequently attributive, especially in "key telephone system".