Passacaglia and Fugue in C minor (BWV 582) is an organ piece by Johann Sebastian Bach. Presumably composed early in Bach’s career, it is one of his most important and well-known works, and an important influence on 19th and 20th century passacaglias: Robert Schumann described the variations of the passacaglia as “intertwined so ingeniously that one can never cease to be amazed.”

https://en.wikipedia.org/wiki/Passacaglia_and_Fugue_in_C_minor,_BWV_582

Bernardo Storace, last bars of Passagagli sopra A la mi re and beginning of Passagagli sopra C sol fa ut, from Selva di varie compositioni(Venice, 1664)

The passacaglia (/pæsəˈkɑːliə/; Italian: [pasːaˈkaʎːa]) is a musical form that originated in early seventeenth-century Spain and is still used today by composers. It is usually of a serious character and is often, but not always, based on a bass-ostinato and written in triple metre.

https://en.wikipedia.org/wiki/Passacaglia

A concertino, literally “little ensemble”, is the group of soloists in a concerto grosso. This is opposed to the ripieno and tutti which is the larger group contrasting with the concertino.

Though the concertino is the smaller of the two groups, its material is generally more virtuosic than that of the ripieno. Further, the concertino does not share thematic material with the ripieno, but presents unique ideas. This contrast of small group to large group and one thematic group against another is very characteristic of Baroque ideology—similar to terraced dynamics where the idea is significant contrast.

https://en.wikipedia.org/wiki/Concerto_grosso#Concertino