To speak off the cuff, that is, without preparation; off the cuff to the lecture - again, not preparing for it specially; spur of the moment to organize a fun evening with friends without the hassle and invitations. Each of you probably heard the word impromptu in a similar value. It is used in music, and is it similar to the familiar.
Latin expromtus - ready, quick, as applied to musical creativity refers to the piece, composed immediately, without preparation. The word is related improvisation in everyday speech, in those examples, with which he began his explanation, can be replaced. In music improvisation and improvisation - concepts are related, but have differences. Improvising musician, as a rule, directly at the concert, when the audience, and there is improvisation only at this time - his first and only sound. On the spur of the composer calls the piece, creating improvisational, he wrote. So, all music lovers know the Schubert impromptus.
Franz Schubert. Impromptu No. 3 Ges-dur Op.90
Franz Schubert. Impromptu No. 4 As-dur Op. 90