The Collaborative International Dictionary of English v.0.48:

internship \in"tern*ship\ ([i^]n"t[~e]rn*sh[i^]p), n.
   1. (Med.) The state of being an intern; the position of an
      intern.
      [PJC]

   2. The period of time during which a person is an intern; as,
      she served her internship over the summer.
      [PJC]

   3. A program to provide novices in a field with
      apprenticeship training.
      [PJC]

   4. The period of time during which a novice in a field serves
      in a subordinate capacity and continues to gain
      experience; the learning period before one becomes an
      expert.
      [PJC]

WordNet (r) 3.0 (2006):

internship
    n 1: the position of a medical intern