By definition, the hurdy-gurdy is a stringed musical instrument. The strings are rubbed by a wheel which is turned by a crank with the right hand of the musician while the left hand plays the melody on the keys.
The origins of the hurdy-gurdy go back up to the tenth century with the invention of the organistrum. This medieval musical instrument has strings which are rubbed by a wooden wheel and was played by two musicians at once: one turned the crank while another pulled the keys upward to change the musical pitch of the melody strings.
More information about functioning, the strings and terminology (diagram) on the FREE lesson: The first meeting with the Hurdy-Gurdy.