In music, a fugue (pronounce /ˈfjuːg/) is a type of contrapuntal composition or technique of composition for a fixed number of parts, normally referred to as "voices". In the Middle Ages, the term was widely used to denote any works in canonic style; by the Renaissance, it had come to denote specifically imitative works. Since the 17th century, the term fugue has described what is commonly regarded as the most fully developed procedure of imitative counterpoint. A fugue opens with one main theme, the subject, which then sounds successively in each voice in imitation; when each voice has entered, the exposition is complete; this is occasionally followed by a connecting passage, or episode, developed from previously heard material; further "entries" of the subject then are heard in related keys. Episodes (if applicable) and entries are usually alternated until the "final entry" of the subject, by which point the music has returned to the opening key, or tonic, which is often followed by closing material, the coda. In this sense, fugue is a style of composition, rather than fixed structure. Though there are certain established practices, in writing the exposition for example, composers approach the style with varying degrees of freedom and individuality.