The Collaborative International Dictionary of English v.0.48:

Specialization \Spe`cial*i*za"tion\, n.
   1. The act of specializing, or the state of being
      spezialized.
      [1913 Webster]

   2. (Biol.) The setting apart of a particular organ for the
      performance of a particular function. --Darwin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

specialization
    n 1: the act of specializing; making something suitable for a
         special purpose [syn: specialization, specialisation]
    2: the special line of work you have adopted as your career;
       "his specialization is gastroenterology" [syn:
       specialization, specialisation, specialty,
       speciality, specialism]
    3: (biology) the structural adaptation of some body part for a
       particular function; "cell differentiation in the developing
       embryo" [syn: specialization, specialisation,
       differentiation]