syn·chro·nized swim·ming in BRIT, also use synchronised swimming Synchronized swimming is a sport in which two or more people perform complicated and carefully planned movements in water in time to music. a sport in which swimmers move in patterns in the water to music. Swimming sport in which the movements of one or more swimmers are synchronized with a musical accompaniment. The sport developed in the U.S. in the 1930s and was admitted as an Olympic event (solo and duet only) in 1984; in 1996 the rules were changed to allow only teams of eight women. Teams are judged on compulsory and optional routines