Tenor is the term given to the highest of male vocal types. Tenors sing the higher pitches of the male voice most comfortably and exhibit a lighter sound than other male voices. In the classical genre, a tenor can be subcategorized as dramatic, light-lyric, lyric or lyric-dramatic depending on tone quality.
Baritone is the middle range, medium-toned male vocal type. The baritone has qualities of both a tenor and bass voice, falling somewhere in the middle. The average baritone should be able to sing lower than a tenor and higher than a bass with ease.
Bass is the lowest of male vocal types. A bass singer is comfortable hitting low tones that go well under what a baritone can sing. The bass voice should also contain a thick, heavy tone that carries a penetrating resonation.
Soprano is the highest female vocal type. Like the tenor, a soprano's voice register can easily cover higher pitches and is unlikely to be as comfortable singing very low. Soprano, however, is a broad term that can be broken down into subcategories such as dramatic and lyric according to vocal tone.
The mezzo-soprano is a middle female vocal type similar to the baritone type. A mezzo-soprano can sing low pitches more easily than a traditional soprano yet cannot hit the highest pitches of a soprano voice. The term mezzo-soprano means "half-soprano" in Italian.
Contralto, or alto, is the term for the lowest female vocal type. According to the website for the San Diego Opera, a true contralto voice is rare, being both low in range and accompanied by a deep, dark sound quality often imitated by mezzo-sopranos.