A serial comma (or some call it Oxford comma) is a comma that precedes a coordinating conjunction such as and. Take a look at this example:
I love chocolate, cheese, and coke.
The serial comma comes after the word cheese.
In writing, serial comma is a part of the style guide. People are often indecisive whether or not they should use the serial comma because some guides advise the usage (mostly in British English writings) and the others do not. Though it is an issue of writing style and the usage can be seen as a matter of personal preference, the usage is still reasonably advisable to avoid misreading and ambiguities. Consider the following example:
I love my parents, Albert Camus and Sylvia Plath.
The omission gives away the sense that “my parents” are Albert Camus and Sylvia Plath. In fact, the meaning intended was the three people that “I” admire.
How to avoid such problem? Use serial comma, or you can work a little harder to reorder the items listed. The sentence can be rewritten as follows:
I love Sylvia Plath, Albert Camus, and my parents.
Voila! It is now easier to digest, isn’t it?