A telephone operated by means of buttons on a keypad rather than a dial; (now) specifically one of several such phones forming an interconnected system in a business, etc.; = key telephone; frequently attributive, especially in "key phone system".
Origin
1950s; earliest use found in Popular Science.
Definition of key phone in US English:
key phone
noun
A telephone operated by means of buttons on a keypad rather than a dial; (now) specifically one of several such phones forming an interconnected system in a business, etc.; = key telephone; frequently attributive, especially in "key phone system".