Partita (also Partia, in German) was originally the name for a single-instrumental piece of music (16th and 17th centuries), but Johann Kuhnau (Thomaskantor till 1722, followed by Bach) and later German composers (notably Johann Sebastian Bach) used it for collections of musical pieces, as a synonym for suite.
Johann Sebastian Bach wrote two sets of Partitas for different instruments. Those for solo keyboard the composer published as his Opus 1 (known as the Klavierübung I). One additional suite in B minor, the Overture in the French Style (often simply called French Overture) is sometimes also considered a Partita. Bach’s Partitas are very rarely called the “German Suites”, in analogy with the national naming of the English and French Suites. See Partitas for keyboard (825–830) and choral partitas for organ. The “Partita” in A minor for solo flute (BWV 1013) which takes the form of a suite of four dances, has been given the title “partita” by its modern editors; it is sometimes transposed for oboe.
Bach also wrote three partitas for solo violin in 1720 which he paired with sonatas. (He titled each of them by the German “Partia”, but they came to be called by the Italian “Partita”, which was introduced in the Bach Gesellschaft edition in 1879, being the more common term at the time.) See: Sonatas and partitas for solo violin.