A keyboard (organ, harpsichord) composition in free, idiomatic keyboard style, employing full chords and running passages, with or without the inclusion of sections in imitative style (fugues).  The earliest toccatas, by A. Gabrieli, consist of full chords and interlacing scale passages only.  To consider them merely virtuoso pieces (as many writers have) is scarcely appropriate, since the passages are decidedly expressive, particularly if played in the free tempo typical of the toccata.

The toccata became organized into alternating toccata (free, idiomatic keyboard style) and fugal sections, usually arranged T F T F T.  With Alessandro Scarlatti, the Italian toccata became the arena for empty keyboard virtuosity and soon declined into a type very similar to the etudes of the early 19th century (Clementi).  The development of the form in Germany, especially the toccatas of Bach, retain the alternating scheme between free and contrapuntal style.

About 1600, the name toccata was also used for a festive brass fanfare, e.g., in the introduction of Monteverdi's "Orfeo" (1607).  The reason for using the name for pieces so different from the keyboard toccata is not clear.  Possibly the latter connotation is bound up with the use of kettle drums for the bass part (typically found in the Toccato form).