Overview

The banjo has a tambourine-like body with a hoop and a screw that secure the vellum belly to the frame. Screw stretchers are used to vary the tension of the belly. The strings pass over a violin-type, or pressure, bridge and are hitched to a tailpiece. The earliest banjos had four gut strings; later, from five to nine metal strings were used. The standard banjo has five metal strings. Four are tuned from the head, usually to C′–G′–B′–D″ upward from (notated) middle C. Preceding the C string is the chanterelle (drone, or thumb), a shorter string fastened to a screw midway in the banjo neck. It is tuned to the (notated) second G above middle C. The actual pitch is an octave lower than notated. Variants of the standard banjo abound. Banjos played with a plectrum, or pick, rather than fingers lack the chanterelle. On a zither banjo the vellum is suspended in a resonator that throws the sound forward; the chanterelle, tuned from the head, passes under the fingerboard to emerge at the fifth fret. The banjo is widely played in U.S. folk music and has also been used in jazz ensembles.

source - https://www.britannica.com/art/banjo-musical-instrument