The Oxford comma (also known as the ‘serial comma’) is the comma that separates the second to last item in a list from a final item that is introduced by ‘and’ or ‘or.’ It is optional...but be aware that not using the serial comma can result in some ambiguity. | Merriam-Webster Dictionary

What is the ‘Oxford Comma’ and why does it cause such a stir? 🤔 The Oxford comma is often used before the last item in a list of three or more items, before ‘and’ or ‘or’. Some like to use it, and some don't. Will you? | Learning English with Oxford