D defs.my
Entry 2 senses Webster, 1913

Improvisation

/ĭmˌ-präv-ĭz-āsh'-ən/ · Im·prov·i·sa·tion · IPA /ɪmˌpɹɑvəˈzeɪʃən/
01 n. The act or art of composing and rendering music, poetry, and the like, extemporaneously; as, improvisation on the organ.
  1. 1.
    The act or art of composing and rendering music, poetry, and the like, extemporaneously; as, improvisation on the organ.
  2. 2.
    That which is improvised; an impromptu.