NOUN (3)

1. an actress who specializes in playing the role of an artless innocent young girl;

2. an artless innocent young girl (especially as portrayed on the stage);

3. the role of an innocent artless young woman in a play;

The Collaborative International Dictionary of English v.0.48:

Ing'enue \In`g['e]`nue"\ ([a^]N`zh[asl]`n[.u]"), n.; pl.
   -nues. [F., fem. of ing['e]nu ingenious.]
   An ingenuous or na["i]ve girl or young woman, or an actress
   representing such a person.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

ingenue
    n 1: an actress who specializes in playing the role of an
         artless innocent young girl
    2: an artless innocent young girl (especially as portrayed on
       the stage)
    3: the role of an innocent artless young woman in a play