A local growth of the outer layer of the skin (the epidermis) caused by a virus. The virus of warts (a papillomavirus) is transmitted by contact. The contact can be with a wart on someone else or one on oneself (autoinoculation).

Warts that occur on the hands or top of the feet are called "common warts."
A wart on the sole (the plantar surface) of the foot is a plantar wart (and can be quite painful).