[…] a serial comma (also called a series comma, Oxford comma, or Harvard comma) is a comma placed immediately after the penultimate term (i.e., before the coordinating conjunction, such as and or or) in a series of three or more terms.

(“Serial Comma” 2022)

Examples:

  • Incorrect: “To my parents, Abraham Lincoln and God.”
  • Correct: “To my parents, Abraham Lincoln, and God.”

Note that serial commas are not a fix-all for ambigious sentences. They may, in fact, introduce ambiguity (“Serial Comma” 2022).

Bibliography

“Serial Comma.” 2022. Wikipedia, January. https://en.wikipedia.org/w/index.php?title=Serial_comma&oldid=1067846637.