allegro [I]—fast, lively tempo. From the Italian word for cheerful or gay.
andante [I]—moderately slow tempo (e.g. walking). Faster than adagio but slower than allegretto
assai—very much. Intensifies the direction of its neighboring words, e.g. "allegro assai", very fast
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
con [I,S]—with
moto, con moto, di moto—motion, with motion. Somewhat more lively than its context would suggest, e.g. "andante con moto", a little more lively than andante
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
quartet, quatuor [F], quartett [G], quartetto [I], cuarteto [S]—ensemble or work for four players the most important examples being the string quartet and the piano quartet
religioso [I]—Religiously
string quartet, Streichquartett [G], quatuor à cordes [F], quartetto d'archi [I], quartetto di cordi [I], cuarteto de cuerda [S], vonósnégyes [H]—ensemble or a work written for that ensemble comprising 2 violins, viola, and cello. This is one of the essential genres/forms/ensembles of chamber music and arguably a critical "core" of "classical" music. Explore the string quartet | wiki