allegretto—moderately quick tempo. slower than allegro but faster than andante
andante [I]—moderately slow tempo (e.g. walking). Faster than adagio but slower than allegretto
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
obbligato [I], obligé [F]—required, necessary, indispensable, obligatory. For instrumentation, the part is required (vs. ad libitum). When associated with Baroque continuo parts, it requires a specific instrument. When used with a keyboard part (e.g. Bach), it may imply a literal, thoroughly written out part vs. the more usual "improvised" (e.g. realized) continuo part at the discretion of the performer.
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
rondo—sectional movement form featuring a recurring refrain between contrasting episodes in a variety of plans, a typical one being ABACABA (A is the refrain; B and C are episodes). Often used for finales.
string trio, Streichtrio [G], Trio d'archi [I], Trio à cordes [F], Trío de cuerdas [S]
—a work for three stringed instruments, most commonly violin, viola and cello. A more rarefied form than the string quartet perhaps because the texture is sparse (each instrument highly exposed) and the means more difficult for natural harmonic richness. But these become challenges and assets in the great trios. Trios almost always emphasize countrapuntal writing with each of the three players in strong relief.