Unilateral exercise means doing an exercise with only one side of your body at a time. For example, instead of doing a regular squat with both legs at the same time, you would do a lunge where you step forward with one leg and bend your knee down to the ground, then step back and switch to the other leg. This way, you are focusing on working each leg individually and helping to balance out any muscle imbalances you may have. It also helps to engage your core muscles more since you have to stabilize your body with only one side working at a time.