In modern usage, the lowest pitch range of the female voice, usually spanning from F or G below Middle C, up more than an octave to D above High C. The word is Italian for “high.” As used in the 16th to 18th centuries, alto referred to a high male part in church music, sung above the tenor. The part was often sung by boys. As music evolved and included female singers, men were still called altos and women were called contraltos. That term is still used in modern classical music, particularly in opera.
“Alto” is also used to describe various instruments that have the same approximate range as the alto voice, such as the alto flute and alto saxophone. French and Italian music scores call the viola (the string instrument second highest in pitch to the violin) an “alto.”