Why is Zotero adding an a or b after the date?

elizabethdulemba

I'm going back through my dissertation to check my citations, and oftentimes, Zotero is adding an a or b after the year in my citation: ex. 2011a, p. 12. Any idea why?

emilianoeheyns

This usually indicates that the same author published multiple works in the same year, and the post-fix disambiguates them in the bibliography.