A joint is where two or more bones are joined together. Joints can be rigid, like the joints between the bones in your skull, or movable, like knees, hips, and shoulders. Many joints have cartilage on the ends of the bones where they come together. Healthy cartilage helps you move by allowing bones to glide over one another. It also protects bones by preventing them from rubbing against each other. Keeping your joints healthy will allow you to run, walk, jump, play sports, and do the other things you like to do. Physical activity, a balanced diet, avoiding injuries, and getting plenty of sleep will help you stay healthy and keep your joints healthy too.