The serial comma, sometimes referred to as the series or Oxford comma, is used immediately in front of a coordinating conjunction, usually “or,” “and,” or “nor,” that precedes the last item, word or phrase in a list or series.
It is important to check with the style guide applicable to what you are writing to determine whether the use of this comma is required or optional. General grammar usage does not dictate that you must use the serial comma; it is optional except in cases where it provides clarity.
The MLA style guide requires the use of the serial comma for example. However, when writing for Write.com, the style guide dictates the elimination of the serial comma unless it provides necessary clarity for the series or list to make sense. Consider the following examples:
Including the serial comma:
Excluding the serial comma:
In an instance where a style guide, as is the case with Write.com, wants the serial comma omitted or you prefer omitting it for general purposes, one is sometimes necessary to provide clarity, as is the case with the below example:
Omitting the serial comma in this instance makes it unclear whether her favorite pancakes are apple pancakes and blueberry-banana pancakes or apple pancakes, blueberry pancakes and banana pancakes. Including the comma makes this clearer, as is demonstrated with the below example:
You can also provide clarity by including the word “pancakes” after each type, although this can prove a bit cumbersome to read for your readers.