Tenor banjos are 4 string banjos that have a shorter neck and come in two varieties, the 17 fret and the 19 fret. The name “tenor” has nothing to do with a lower pitch such as a vocalist who is a tenor or a tenor saxophone. No one knows for sure where the name tenor came from, but many believe it was a mistake somewhere in history as these type of banjos were used during the American tango craze of the early 20th century and were often called tango banjos. Tango then erroneously became tenor somewhere down the line.
Tenor banjos are generally used for jazz or Irish music. You can find them used in a Jamaican form of music called Mento, a predecessor to reggae, and Moroccan music. In both of these types of music you also see plectrum banjos being used, or 5 string banjos without the 5th string on them.
Tenor banjos are tuned in the musical interval of fifths. This is the same as the string family in an orchestra - violins, violas, and cellos (except the bass).
There are two common ways to tune them - both using fifths.
Standard Tenor Tuning - C, G, D, A
Irish Tenor Tuning - G, D, A, E - same as mandolin and violin!