Informal designating, or characterized by, the close harmony of usually male voices, esp. in sentimental songs: a barbershop quartet
See barbershop in American Heritage Dictionary 4
(bärˈbər-shŏpˌ)
noun
The place of business of a barber.
adjective
Of, consisting of, or relating to the performance of sentimental songs for unaccompanied, usually male voices in four-part harmony: a barbershop quartet.