Ingrown toenail: A common disorder that occurs when the edge of the toenail grows into the skin of the toe particularly on the big (great) toe. The corner of the nail curves down into the skin, often due to mis-trimming of the nail, or due to shoes that are too tight. An ingrown toenail can be painful and lead to infection.
Sometimes simply removing the corner of the nail from the skin is enough to cure this problem, although you may need to have this done by a doctor, podiatrist, or foot-care specialist. If there is infection present, that also requires treatment. In some cases the entire nail must be removed. If ingrown toenails are caused by congenital nail malformations, the nail bed can be treated to permanently prevent regrowth. Known also as onychocryptosis and unguis incarnatus.