Relax is a verb that describes feeling less stressed out or tense. If you want to relax after a crazy day at school, you might watch TV, take a nap, or do yoga to help you unwind.
Relax can also refer to behavior that grows less formal or restrained, like a beach wedding where the bride and groom relax the usually formal ceremony by wearing casual clothing. Relax can also mean to become less tight. When you relax your grip on a pen, your hold loosens up. Relax can also refer to something that becomes less severe or strict. If your teacher would relax the attendance rules, you wouldn't keep getting in trouble for skipping class!