Lowest Female Singing Voice

Word Meaning:

CONTRALTO — (music) The lowest female voice or voice part, falling between tenor and mezzo-soprano. The terms contralto and alto refer to the same musical pitch range, but among singers, the term contralto is reserved for female singers; the equivalent male form is counter-tenor. Originally the contratenor altus was a high countermelody sung against the tenor or main melody.

Definitions from Wiktionary.