a. A saucy, coquettish, intriguing maidservant in comedies or comic opera.
b. An actress or a singer taking such a part.
So some soubrettes in opera are Zerlina, Despina and Adele. Marilyn Monroe was playing a soubrette. It is a character type more than it is a voice category. Audrey Hepburn was a kind of serious soubrette. Paris Hilton is a soubrette, money notwithstanding.
There seems to be some confusion on this topic. I am acquainted with an aging soubrette who does not know what to do now. Become a lyric soprano.