Musical improvisation (also known as musical extemporization) is the creative activity of immediate (""in the moment"") musical composition, which combines performance with communication of emotions and instrumental technique as well as spontaneous response to other musicians. Sometimes musical ideas in improvisation are spontaneous, but may be based on chord changes in classical music, and many other kinds of music. One definition is a ""performance given extempore without planning or preparation."" Another definition is to ""play or sing (music) extemporaneously, by inventing variations on a melody or creating new melodies, rhythms and harmonies.""Encyclopædia Britannica defines it as ""the extemporaneous composition or free performance of a musical passage, usually in a manner conforming to certain stylistic norms but unfettered by the prescriptive features of a specific musical text. Music originated as improvisation and is still extensively improvised in Eastern traditions and in the modern Western tradition of jazz.""Throughout the Medieval, Renaissance, Baroque, Classical, and Romantic periods, improvisation was a highly valued skill. J.S. Bach, Handel, Mozart, Beethoven, Chopin, Liszt, and many other famous composers and musicians were known especially for their improvisational skills. Improvisation might have played an important role in the monophonic period. The earliest treatises on polyphony, such as the Musica enchiriadis (ninth century), make plain that added parts were improvised for centuries before the first notated examples. However, it was only in the fifteenth century that theorists began making a hard distinction between improvised and written music. Many classical forms contained sections for improvisation, such as the cadenza in concertos, or the preludes to some keyboard suites by Bach and Handel, which consist of elaborations of a progression of chords, which performers are to use as the basis for their improvisation. Handel, Scarlatti, and Bach all belonged to a tradition of solo keyboard improvisation.In Indian, Pakistani, and Bangladeshi classical music, raga is the ""tonal framework for composition and improvisation."" The Encyclopædia Britannica defines a raga as ""a melodic framework for improvisation and composition.