A term used to classify a composition in relation to the composer's other compositions. Abbreviated as " Op. " (work) or " Opp. " (works), compositions are typically given an opus number in cronological order (i.e. " Op. 1", " Op. 2", etc.). Because the Opus numbers are often assiged by publishers, they are not always a reliable indication of the chronology of the composition."work". With a number, used to show the order in which the works by a given composer were written or published. Opus numbers are most often used for composers who catalogued their own works.<br><br>A musical composition, or group of compositions, usually numbered to indicate the order of its publication within a composer's entire output.