'Improvisation' definitions:

Definition of 'improvisation'

From: WordNet
noun
A creation spoken or written or composed extemporaneously (without prior preparation)
noun
An unplanned expedient [syn: improvisation, temporary expedient]
noun
A performance given extempore without planning or preparation [syn: extemporization, extemporisation, improvisation]

Definition of 'Improvisation'

From: GCIDE
  • Improvisation \Im*prov`i*sa"tion\, n. [Cf. F. improvisation.]
  • 1. The act or art of composing and rendering music, poetry, and the like, extemporaneously; as, improvisation on the organ. [1913 Webster]
  • 2. That which is improvised; an impromptu. [1913 Webster]

Synonyms of 'improvisation'

From: Moby Thesaurus