The Collaborative International Dictionary of English v.0.48:

Hyperplasia \Hy`per*pla"si*a\, n. [NL., fr. Gr. "ype`r over + ?
   conformation, fr. ? to mold.] (Med. & Biol.)
   An increase in, or excessive growth of, the normal elements
   of any part.
   [1913 Webster]

   Note: Hyperplasia relates to the formation of new elements,
         hypertrophy being an increase in bulk of preexisting
         normal elements. --Dunglison.
         [1913 Webster]

WordNet (r) 3.0 (2006):

hyperplasia
    n 1: abnormal increase in number of cells