In opera what does op 77 or 35 mean?

In opera, the term "Op. 77" or "Op. 35" refers to the opus number of a particular musical composition. An opus number is a unique identifier assigned to a composer's work, typically in chronological order of publication or composition.

For example, if a composer writes an opera and gives it the opus number "Op. 77," it indicates that it is their 77th published or composed work. Similarly, "Op. 35" means that it is the composer's 35th published or composed work.

Opus numbers are used to help catalog and organize a composer's body of work, making it easier to reference and identify specific compositions. They are often included in the title or description of the piece, along with the composer's name and other relevant information.

By using opus numbers, music scholars, performers, and enthusiasts can easily identify and discuss specific compositions, track a composer's development over time, and gain a deeper understanding of their musical output.