What is the meaning of Headstock?

A headframe.

A part of a machine (such as a lathe or drill) that contains the primary spindle.

A beam that supports a bell.

A clamp that restrains a cow by the neck.

The part of a lute-type string instrument, such as a guitar, that holds the tuning pegs or tensioning screws of the strings.

A transverse structural member at the extreme end of a rail vehicle's underframe, also used on some bogies.

Source: wiktionary.org