Tenor banjos (4 strings)

Tenor banjos have four strings. Usually, they are tuned in fifths. Either in C, G, d, a, or G, D, a, e
Usually one finds tenor banjos especially in the Irish Folk (mostly in G, D, a, e - tuning), used as a melody instrument, whereas with New Orleans style jazz or Dixieland, it's typically used as chord accompaniment in CGDA tuning. Many Jazzmen tune it one tone flat, though. The reason is that most jazz pieces are in Bb or Eb, thus the altered tuning allows the player to use more familiar chord grips.