"The serial comma (also known as the Oxford comma or Harvard comma) is the comma used immediately before a grammatical conjunction (nearly always and or or; sometimes nor) that precedes the last item in a list of three or more items. For example, a list of three countries might be indicated by the phrase "Portugal, Spain, and France", which is written with the serial comma, or by the phrase "Portugal, Spain and France", which is written without it.
There is no global consensus among writers or editors on the use of the serial comma. Most authorities on American English recommend its use, but it is not so frequently used in British English (see extended treatment below, including a survey of published recommendations in Usage and subsequent sections). In many languages (e.g., French, German, Italian, Polish, Spanish) the serial comma is not normally used, although it may be employed in cases where it aids clarity or the prosody to be used when reading."
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