Source : Webster's Revised Unabridged Dictionary (1913)

Extemporization \Ex*tem`po*ri*za"tion\, n.
   The act of extemporizing; the act of doing anything
   extempore.

Source : WordNet®

extemporization
     n : a performance given extempore without planning or
         preparation [syn: {extemporisation}, {improvisation}]