IMPROVISATION
extemporization, extemporisation, improvisation
(noun) a performance given extempore without planning or preparation
improvisation, temporary expedient
(noun) an unplanned expedient
improvisation
(noun) a creation spoken or written or composed extemporaneously (without prior preparation)
Source: WordNet® 3.1
Etymology
Noun
improvisation (countable and uncountable, plural improvisations)
The act or art of composing and making music, poetry, and the like, extemporaneously
That which is improvised; an impromptu.
Musical technique, characteristic of blues music.
The act of improvising, acting or going about something without planning ahead
Source: Wiktionary
Im*prov`i*sa"tion, n. Etym: [Cf. F. improvisation.]
1. The act or art of composing and rendering music, poetry, and the
like, extemporaneously; as, improvisation on the organ.
2. That which is improvised; an impromptu.
Source: Webster’s Unabridged Dictionary 1913 Edition