Commas are one of the most abused punctuation marks. One of the more confusing is the serial comma. Also known as a series comma or the Oxford comma, a serial comma is used before the conjunction that joins the last two elements in a series. For example:
Chris, Michael, and Henry gave many consultations at the last education program.
My great-grandfather’s main crops were barley, peas, and turnips.
When the elements in the series have internal punctuation, it is usually easier to separate the elements with a semi-colon instead of a comma:
Their children were Steven, b. 1862; Jonathan, b. 1864; Mary, b. 1866; and Louisa, b. 1868.
For more information on the proper use of serial commas, see the Chicago Manual of Style, 16th edition.