Tenor is the highest male voice.
The name "tenor" derives from the Latin word tenere, which means "to hold". In medieval and Renaissance polyphony between about 1250 and 1500, the tenor was the structurally fundamental (or ‘holding’) voice, vocal or instrumental. All other voices were normally calculated in relation to the tenor, which often proceeded in longer note values and carried a borrowed Cantus firmus melody. Until the late 15th-century introduction of the contratenor bassus, the tenor was usually the lowest voice, assuming the role of providing a harmonic foundation. It was also in the 15th century that "tenor" came to signify the male voice that sang such parts.
Several famous tenors include: Placido Domingo, Jose Carreras, and Luciano Pavarotti.
Tenor Notes:
(Graphic used with permission from Wikipedia)
If you want to learn more about the tenor voice, visit these links:
http://192.107.108.56/portfolios/m/myhren_s/FINALP/index.htm
http://en.wikipedia.org/wiki/Tenor