The Supremes, e.g. (4)
I believe the answer is:
trio
(Other definitions for trio that I've seen before include "Beethoven's 'Archduke': famous piece written for this ensemble" , "Bee Gees, Supremes or Andrews Sisters, say" , "(Composition for) three performers" , "Group of three (musicians)" , "Beethoven's 'Archduke', for example" .)