The four competitive strokes are (1) freestyle, (2) backstroke, (3) breaststroke, and (4) butterfly. Events are held in all of the competitive strokes at varying distances depending on the age-group of the swimmer. In addition, there is a combination of the strokes swum by one swimmer called the individual medley (IM). Other swimming events include relays, which are a group of four swimmers who either all swim freestyle (freestyle relay) or each swim one of the competitive strokes in the order of backstroke, breaststroke, butterfly and freestyle (medley relay).