The 100 IM (Individual Medley) and 100 Medley Relay are both races that incorporate all four strokes—butterfly, backstroke, breaststroke, and freestyle—but they differ in format and execution.

• 100 IM: This is an individual race where a single swimmer completes 25 meters or yards of each stroke in the following order: butterfly, backstroke, breaststroke, freestyle. The swimmer transitions between strokes at each wall, following specific rules for turns. If your swimmer wants to swim the 100IM, they must be able to swim all 4 strokes. If your swimmer is interested in swimming the 100IM, have them reach out to a coach at practice. 

• 100 Medley Relay: This is a team event with four swimmers, each swimming one stroke for 25 meters or yards. The order is different from the IM: backstroke, breaststroke, butterfly, freestyle. The backstroke starts in the water, while the other swimmers dive in from the blocks.

More information can be found here if you need additional clarification.