A prelude is a short piece of music, the form of which may vary from piece to piece. While, during the Baroque era, for example, it may have served as an introduction to succeeding movements of a work that were usually longer and more complex, it may also have been a stand-alone piece of work during the Romantic era. It generally features a small number of rhythmic and melodic motifs that recur through the piece. Stylistically, the prelude is improvisatory in nature. The term may also refer to an overture, particularly to those seen in an opera or an oratorio.