The Collins dictionary definition of the Oxford comma is “a comma between the final items in a list, often preceding the word and or or, such as the final comma in the list newspapers, magazines, and books”.
The history of the Oxford comma (also known as the serial comma or Harvard comma) is a little unclear, but it has been attributed to Horace Hart a printer and controller at Oxford University Press (OUP) from 1893 to 1915. Hart introduced it in his style guide Hart’s Rules for Compositors and Readers—a guide he wrote in 1905 for OUP employees. However, at that time it was not called the Oxford comma. It wasn’t until 1978 that Peter Sutcliffe named it the Oxford comma in his book The Oxford University Press: An Informal History.
The use of the Oxford comma is a much-debated punctuation mark. Lynne Truss (author of Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation) says: “There are people who embrace the Oxford comma, and people who don’t, and I’ll just say this: never get between these people when drink has been taken.“ However, many style guides such as the Chicago Manual of Style and the Oxford University Press House Style, do advocate its use because it helps to avoid ambiguity and confusion. For example,
Philip visited his parents, John and Millie.
Philip visited his parents, John, and Millie.
Without the comma after John, these two sentences have very different meanings. In the first sentence, Philip appears to have visited two people (his parents who are called John and Millie). In the second sentence (which includes an Oxford comma), Philip visited four people (his parents and John and Millie). By adding the comma after John and before and, it is clear that John and Millie are not Philip’s parents but two separate people. This sentence could be re-written as Philip visited John, Millie and his parents which avoids ambiguity but equally why not just insert an Oxford comma. It’s not that hard.
Here is another example:
Michael went on holiday with his brother, an artist and a musician.
Michael went on holiday with his brother, an artist, and a musician.
Without the added comma we may reasonably assume that Michael went on holiday with his brother who is both an artist and a musician. However, by inserting an Oxford comma after artist and before and, we conclude that Michael actually went on holiday with three other people —his brother, a second person who is an an artist and a third person who is a musician.
Perhaps you would prefer not to be bothered with yet another rule of grammar and can’t see what all the fuss is about. However, because the Oxford comma was introduced to make a sentence clear and unambiguous, it is worth considering using it. Even though the history of it may be uncertain, the reasons for using it are much clearer.