Impressionism was a term at first used mockingly to describe the work of the French painter Monet and his circle, who later made use of the word themselves. It was similarly used to describe an element of vagueness and imprecision coupled with a perceived excess of attention to colour in the early music of Debussy, who did not accept the criticism or the label, although his harmonic innovations and approach to composition have points in common with the ideals of Monet.
The word impromptu was first used as a title for a musical composition in 1822 by the Bohemian composer Vorisek for six piano pieces, to be imitated by Schubert's publisher in naming a set of four piano Impromptus, to be followed by four more, perhaps so named by the composer. Chopin used the title for four compositions in this seemingly improvised form, and there are further impromptus by other composers from that period onwards, generally, but not always, for a single instrument.
Improvisation was once a normal part of a performer's stock-in-trade. Many of the greatest composer-performers, from Bach to Mozart and Beethoven, were masters of improvisation, but in the 19th century this became a less common part of public performance, although it remained and remains a necessary skill for a church organist, traditionally required to provide a musical accompaniment of varying length to liturgical ritual.
Instrumentation is generally used to mean orchestration, the art of writing music for instruments, or, alternatively, the actual scoring of a particular composition.
In the theatre an interlude performs the same function as an entr'acte, music between acts or scenes, designed to bridge a gap. It may also be used to indicate music played or sung between two other works or two sections of a work.
Earlier signifying a comic interlude inserted between the acts of an opera seria, the 19th century intermezzo was often either a musical interlude in a larger composition or a piece of music in itself, often for solo piano. In this second sense it is used by Schumann and later by Brahms in their piano music, while both Mendelssohn and Brahms use the word as a movement title in chamber music.
In music an interval is the distance in pitch between two notes, counted from the lower note upwards, with the lower note as the first of the interval. The violin, for example, is tuned in intervals of a fifth, G to D, D to A and A to E, the double bass in fourths, from E to A, A to D and D to G. Harmonic intervals occur simultaneously, as when a violinist tunes the instrument, listening carefully to the sound of two adjacent strings played together. Melodic intervals occur between two notes played one after the other.
Intonation is the exactness of pitch or lack of it in playing or singing. Collective intonation is that of a group of instruments, where slight individual variations in pitch can be lost in a generally more favourable effect.
The two-part Inventions of Johann Sebastian Bach are contrapuntal two-voice keyboard compositions, and the word is often understood in this sense, although it had a less precise meaning in earlier music.
L'istesso tempo, the same speed, is found as an instruction to the player to return to the previous speed of the music.