In punctuation, a serial comma or series comma (also called Oxford comma and Harvard comma) is a comma placed immediately before the coordinating conjunction (usually and, or, or nor) in a series of three or more terms. For example, a list of three countries might be punctuated either as "Portugal, Spain, and France" (with the serial comma), or as "Portugal, Spain and France" (without the serial comma).
Opinions among writers and editors differ on whether to use the serial comma. In American English, a majority of style guides mandate use of the serial comma, including The Chicago Manua...