The Collaborative International Dictionary of English v.0.48:

Prolusion \Pro*lu"sion\, n. [L. prolusio, fr. proludere to
   prelude; pro before + ludere to play: cf. F. prolusion, It.
   prolusione.]
   A trial before the principal performance; a prelude; hence,
   an introductory essay or exercise. "Domestic prolusions."
   --Thackeray.
   [1913 Webster]

         Her presence was in some measure a restraint on the
         worthy divine, whose prolusion lasted.   --Sir W.
                                                  Scott.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prolusion
    n 1: a short introductory essay preceding the text of a book
         [syn: foreword, preface, prolusion]
    2: exercising in preparation for strenuous activity [syn: warm-
       up, tune-up, prolusion]