In classical music, what does "B." stand for?

For example, take Chopin's "Ballade for piano No. 1 in G minor Op. 23, B. 66"

No. is the number, Op. is the opus, what is B. 66 mean?

"B" is the person or persons who compiled the catalogue of Chopin's works - I don't remember what the "B" actually stands for in this case, but it is the catalogue number. Other examples are things like "BWV" (Bach), "D" (Schubert) and "K" or "KV" (Mozart). Some composers like Haydn will have several different catalogue collections, and will have different abbreviations after the opus number depending on which edition you own.

(It is perhaps for the Brown-index numbering of Chopin's works, there are some without opus numbers but having a Brown-index number ex. Nocturne in c minor (op. posth.) is Brown-index 108)

Actually i was not aware of this 'B' symbol, thanks for the questions!

By the way, are you learning Chopin's Ballades? I love this repertoire as well as No. 4 in F minor... They are really capturing, aren't they? keep it up if you are learning or are going to learn! :)

It is to do with the Rythm. I have attached a URL that will prolvide some reading on the subject. It's a very interesting question that you raise.