The middle category of the female (or falsetto male) voice. Though closer to soprano than to contralto, it is marked more by quality of tone (darker or richer than a soprano) than by range, which may include many of the soprano’s high or the contralto’s low notes. The sound of a mezzo-soprano can either be voluptuous (as in the case of Delilah or Carmen) or it can be thinner and more agile (which might describe Rosina in The Barber of Seville). Marilyn Horne, Frederica von Stade and Cecilia Bartoli are some of the better known mezzos of our day.
A middle range female voice.
one who sings in the lower part of the soprano range
The middle female singing voice, lower than soprano, but higher than contralto.
the female singing voice between contralto and soprano
See this page. (Incidentally, this is the same range that the "castri"-the castrated males of the 17th and 18th centuries-sang in.)
Female voice of middle range.
The range of a voice between soprano and alto.
Female singer with a medium-to-low voice range.