Wart: 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). Genital (venereal) warts are located on the genitals and are transmitted by sexual contact; they are a form of STD (sexually transmitted disease).
Warts are nothing new. The word "wart" is from Old English. As far back as the 8th century, a "wart" was, well, a wart.