What does improvisation mean musically

Music lexicon: what does improvisation mean?

Improvisation (1879)

improvisation (from Latin ex impro viso, unexpectedly, surprising), the art of creating a piece of music without any preparation and immediately executing it, which is also denoted by the word "fantasizing" (see there). [Riewe Concise Dictionary 1879, 126]

Improvisation (1882)

improvisation (from the Latin ex improviso, "without preparation"), an impromptu lecture, without preparation, without prior written recording, name for poetic as well as musical instant productions.

Most of the great music masters are also famous as improvisers on the piano or organ. A distinction is made between improvisation and free imagination by understanding that the former is strictly bound to a form. It used to be one of the master rehearsals of a competent musician that he could improvise (extemporise) a fugue on a given topic, in which Bach in particular achieved amazing things. This type of improvisation requires intensive concentration of the mental powers, while so-called fantasizing is a complete release of the imagination and usually results in more kaleidoscopic, colorfully changing mood images. In the middle stands the variation of a given theme, imagination about a melody, an art that every decent musician must be capable of. [Riemann Musik-Lexikon 1882, 411]

Improvisation, improviser, improviser (1840)

improvisation (French), fantasy; Improviser, fantasize, poetry impromptu, sing or play; Improviser, someone who fantasizes (but not in a fever), or, as W. C. Müller puts it, a fantasist. [Gathy Encyclopedia Music Science 1840, 225f]