Air [Fr], Air [E], Ayre [E], Aire, Aria [I]—Song. Traditionally indicates a piece of melodic or vocal nature as opposed to one of dance-like character (i.e. in form or rhythm). An aria typically refers to a formalized song within an opera context for one or more voice
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
divertimento [I], divertissement [F]—amusement, diversion, entertainment, even table music; Typically, a suite of movements (often more than 4), often intended for diversion and pleasure of a lighthearted nature, suitable for social occasions. Typically implies a smaller chamber ensemble. The name was common in the 18th century for a variety of music, some of which was more serious and profound than its title would suggest. The French divertissement can apply to an entr'acte: dances and airs from other acts. wiki
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.
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