The serial comma or series comma is so called as a comma is used immediately before a coordinating conjunction such as ‘and’ and ‘or’ preceding the last item in a list comprising of three or more items. For example:
After land preparation, you may sow, dibble, or drill the seeds.
Please note that most style guides, for example, the CSE Manual for Authors, Editors, and Publishers (CSE, 2014) recommends the use of serial commas. This serial comma is also called Oxford comma or Harvard comma because the Oxford University Press and the Harvard University Press have traditionally been following this type of comma usage in their publications.
The serial comma is recommended for clarity and to avoid misreading. If a particular journal or publishing company insists for serial comma, there is no other option but to follow it!
For a more lighthearted look at punctuation (and the Oxford comma), see the book "Eats, Shoots and Leaves" by Lynne Truss--NY Times best seller, available at Amazon.