Throughout history, the tune of udis the most close to human voice peculiarly by its melancholy and gloomy melodies among musical instruments. Medieval scholars, Farabi and Avicenna have described ud as the most perfect musical instrument. In practice, they answered with their scientific works. This article provides an overview of the ud and its features. Historical sources about the instrument are mentioned. The Arabic-Persian terms used in its setting are explained and analyzed. It also focuses on the instruments that are related toud.