ECO's Essential Guide to Classical Music Terms

We know that classical music has a bunch of terms that can be daunting to new listeners – and confusing to experienced ones!

For those of you who are interested in learning a bit more, please read on… 

OPUS (Op.)

This refers to the whole musical work, which can include multiple “Numbers”. For example, one of Chopin’s most famous works is his Preludes, Op. 28. This collection contains 24 individual “numbers” – so, for example, Op. 28, No. 4 is the highly popular prelude in E Minor. This is in comparison to Chopin’s masterful Sonata Op. 58, which is one work – and while it has four movements, they are not considered individual “numbers”. 

Perhaps one way to think of it is like a modern rock or pop album – the album is the opus and the tracks are the numbers. Pink Floyd’s Dark Side of the Moon might be considered Opus 8 (it’s their eighth studio album), and “Money” (the sixth track on the album) might be considered Number 6. 

So there you have it – Pink Floyd’s “Money” is Op. 8, No. 6!


A sub-unit of a larger musical work such as a symphony or concerto. These are most often named with the Italian term for the tempo (allegro, for example), which also often (but not always) indicate a specific mood. 


Medieval: c. 1150 – 1400

Renaissance: c. 1400 – 1600

Baroque: 1600 – 1750 (JS Bach, Handel)

Classical: 1750 – 1820 (Mozart, Haydn, Early Beethoven)

Early Romantic: 1820 – 1860 (Late Beethoven, Chopin)

Late Romantic: 1860 – 1920 (Brahms, Liszt, Rachmaninoff)

“20th Century”: – 1920 – 1999

Most of the music performed by major orchestras today consists of music from the Baroque, Classical, and Romantic eras – primarily due to its enduring popularity!


 Bach Werke Verzeichnis. Actually it means “Bach’s Catalog of Works” in German!  First published in 1950 and edited by Wolfgang Schmieder, the catalog’s second edition appeared in 1990. 

The BWV catalog is the definitive catalog of all 1,126 of J.S. Bach’s known compositions, including works of doubtful authorship or authenticity. The catalog is organized into the genre of composition, such as his cantatas, passions, oratorios, keyboard works, orchestral works, and others. There is a LOT of music to love when it comes to Bach!

Koechel (K.)

 Similarly to the BWV catalog, the Koechel Catalog is the catalog of Mozart’s works, as collected and organized by the German musicologist Ludvig von Koechel. Mozart published very few actual “opus” numbers during his lifetime, and due to the high level of popularity that his works enjoy (not just those he published), a more complete numbering solution was developed. 

For example, Mozart’s Piano Concerto No. 23 in A Major is K. 488. There are 626 total “K” numbers.