The Collaborative International Dictionary of English v.0.48:

extroversion \ex`tro*ver"sion\, n. [See Extrorse.]
   1. The condition of being turned wrong side out; as,
      extroversion of the bladder. --Dunglison.
      [1913 Webster]

   2. (Psychol.) the trait of being interested primarily in
      things in one's external environement, rather than one's
      own thoughts and feelings.
      [PJC]

   3. (Psychol.) the act of directing one's interests primarily
      toward things in one's external environement, rather than
      one's own thoughts and feelings.
      [PJC]

WordNet (r) 3.0 (2006):

extroversion
    n 1: (psychology) an extroverted disposition; concern with what
         is outside the self [syn: extraversion, extroversion]
         [ant: ambiversion, introversion]