A piece of music written by a major composer usually singular usually followed by a number

Opus is a term commonly used in the field of classical music to refer to a numbered composition or work of a composer. It is derived from the Latin word "opus", meaning "work" or "labor". Each composition or significant piece of music by a composer is assigned an opus number, which serves as a way to identify and catalog their works.

The opus number system allows for easier organization and reference of a composer's output. It helps to distinguish one composition from another and provides a chronological order to the works. Composers often assign opus numbers to their compositions based on the order in which they were composed or published.

Opus numbers are typically indicated using the abbreviation "Op." followed by a number, such as Op. 1, Op. 20, or Op. 73. Sometimes, additional information is added after the number, such as Op. 25 No. 1 or Op. 82/3, to denote specific movements or sections within a larger work.

Opus numbers are especially prevalent in the works of classical composers from the 18th to the 20th centuries, including Ludwig van Beethoven, Franz Schubert, and Johannes Brahms, among many others. These composers often had a large number of compositions, and the opus number system helped to keep their works organized and easily identifiable.

It's worth noting that not all composers or musical traditions use the opus number system. Some composers may use alternative cataloging systems or simply title their compositions without assigning opus numbers. Additionally, composers from non-classical music genres, such as popular music or jazz, often do not use opus numbers to designate their works.

Example of Opus

BEETHOVEN Piano Trio No. 1 in E-flat major (Op. 1, No. 1) Score