The 4-string banjo is a standard banjo without the short drone string. It usually has 22 frets on the neck and a scale length of 26 to 28 inches, and was originally tuned C3 G3 B3 D4. It can also be tuned like the top 4 strings of a guitar (Chicago tuning). It is usually played with a guitar-style pick or plectrum (that is, a single one held between thumb and forefinger), unlike the 5-string banjo, which is either played with a thumbpick and two fingerpicks or with bare fingers. The plectrum banjo evolved out of the 5-string banjo to cater to styles of music involving strummed chords. It is also featured in many early jazz recordings and arrangements. 

4-string banjos can be used for chordal accompaniment (as in early jazz), for single-string melody playing (as in Irish traditional music), in chord melody style (a succession of chords in which the highest notes carry the melody), in tremolo style (both on chords and single strings), and a mixed technique called duo style that combines single-string tremolo and rhythm chords.