telephone set with the mouthpiece and earpiece mounted on a single handle
"She picked up the old handset, noting how its mouthpiece and earpiece were conveniently mounted on a single handle."
The part of a landline telephone containing both receiver and transmitter (and sometimes dial), held in the hand.
"He picked up the handset to answer the ringing call."
In plain English: A handset is the part of an old telephone that you hold up to your ear and mouth to talk on it.
"He placed his finger on the handset to answer the ringing phone."
Usage: A handset is specifically the handheld portion of a traditional landline phone that you hold to your ear or mouth, distinct from the base unit it connects to via a cord. Unlike modern smartphones where these functions are integrated into one device, this term applies only when the receiver and microphone are separate pieces connected by wires.
The word handset is a straightforward combination of "hand" and "set." It was first used to describe the part of a telephone that you hold in your hand while speaking or listening.