barbershop harmony:
"four part, a capella, consonant, close harmony singing with the voices typically in TTBB (tenor 1, tenor 2 [the lead or melody], baritone and bass), and featuring a flexible tempo, a preponderance of dominant seventh-type chords, ringing harmonics, characteristic arranging devices (swipes, tags, etc.) and a commitment to the popular songs of an earlier period in American history (very loosely 1890-1930)".
from "Four Parts, No Waiting" by Gage Averill.