allegretto—moderately quick tempo. slower than allegro but faster than andante
allegro [I]—fast, lively tempo. From the Italian word for cheerful or gay.
chamber music, Kammermusik [G], musique de chambre [F], musica da camera [I], musica cameralis [L]—"Classical Music" for a small ensemble, generally 8 or fewer players with a canonical emphasis on 3-6 players. explore
duo, duet, dueto [S], duetto [I], duett [G]—a work for two instruments; the ensemble itself
grazioso [I], con grazia, gratioso, graziös [G], Mit Grazie—graceful, gracefully; easy
intermezzo, intermedio [S], intermède [F], interlude, Entr'acte—music that is "inserted" (or "interpolated) between two musical entities of greater importance (e.g. movements, acts, verses, etc.). Often suggests music of a lighter character, entertaining contrast or even improvisation.
opus [L], opera[pl], Op., Opp, WoO, Op. posth—work, as in a work of art. For unique identification, publishers/composers often assign an "opus number", abbreviated as "Op." (e.g. Op. 1). A range of works by opus number, uses the plural "opp." (e.g. "Opp. 1-3"). A single opus number may refer to a collection of works (e.g. a set of quartets) giving rise to designations like "Op. 1, No. 4". For misc. works without opus numbers, "WoO" is often used (e.g."Without Opus"). Posthumously assigned numbers may use "Op. posth". Opus numbers may not precisely reflect chronology (publication vs. composition), can be erroneous, sparse or duplicative. Thus, the works of some historically important composers may use separate catalog numbers (e.g. Bach, Haydn, Schubert). See wiki
piano duet, piano four-hands, piano 4-hands—ensemble (work) for 2 players on one piano
tempo, tempi [pl]—speed or pace at which music progresses. Traditional classic music typically uses standard Italian words to designate the tempo, e.g. Allegro or adagio. Metronome markings provide precise numerical speeds. Tempo selection during performance is a complex artistic choice informed by composer's markings, performance tradition, technical limitations and interpretation.