BodyHair
When you hit puberty you will start to grow more body hair. Body hair is just hair that grows on your body?, not so much on your head. It tends to be shorter and thicker than head hair.
Both boys and girls will get more hair on their arms, underarms, chest, legs, and crotch and genitals. Body hair on your crotch and genitals is called pubic hair. (Possibly you could get hair on your back, too. Sorry, boys.) Generally boys and men will grow more body hair than girls and women.
Body hair will not grow and grow out like the hair on your head, it should stay relatively short. Girls and women will usually shave their legs and underarms (and lately maybe their arms and feet, too). I don't advise shaving pubic hair, though it's definitely in fashion among young people nowadays due to pornography.