What does the term opus refer to in relation to music?

The term opus, derived from the Latin word for "work," is primarily used by composers to identify and categorize their compositions. Typically, it precedes a number that indicates the chronological order of the piece in relation to the composer’s output. This labeling helps in organizing and referencing works, especially in discussions about the composer's body of work.

For example, you might encounter a piece referred to as "Symphony No. 1, Op. 5," where "Op. 5" indicates that this is the fifth work cataloged by the composer. This convention provides clarity and assists musicians, historians, and listeners in identifying and understanding the significance of each piece within a composer’s oeuvre.

The other options do not relate to the specific meaning of opus in the context of music composition. While different genres might exist (the first choice), or various notation styles could be employed (the third choice), and performance types might vary (the fourth choice), none of these aspects directly connect to the usage of opus as a designation for a composer’s work.