A) With regard to accompanied vocal music . The term "concerto" was first used during 16th century to refer to vocal compositions accompanied by orchestra or instrumental music, in order to distinguish these pieces from the style of unaccompanied, a capella music. Giovanni Gabrielli's "in ecclesiis" and Heinrich Schutz' s " Saul, Saul, was verfolgst du mich" were considered to be "concerti". The term was used until the Baroque period: for example the " kleine Geistliche Concerte" of Heinrich Schuetz (1636) and several Bach cantatas were called "concerti".
B) With regard to instrumental music. As Willi Apel indicates, during 17th century the term was also referring to instrumental music meaning "contrasting performing bodies playing in alteration". Some authors called this style of the 17th century "modern style" (stile moderno). During 1620-
The Baroque concerto reached its peak between 1670-
Vivaldi: Concerto Grosso in D minor
It is the most important of the three types of Baroque concerto. Regarding the orchestra, it consists of a small group of solo instruments (concertino) and a larger orchestra performing in contrast . The concertino usually consists of two violins and a basso continuo (cello and harpsichord). Baroque trio sonata is consisted of the same set of instruments. The orchestra consists of strings (sometimes, later, winds were included). Corelli's concerti, op 6, are among such compositions . Most of these have 5 or more parts.
Antonio Vivaldi introduced the schema: allegro-
see also: ripieno
Willi Apel, Harvard dictionary of music, second edition, eighth printing.