For non-grammar nerds, the Oxford (serial) comma is the final comma in a list of things.  People either love or hate the Oxford comma, and style manuals are beginning to compromise by advocating use of the Oxford comma as an option when clarity is needed.  I always use it because it always provides clarity.

Without the Oxford comma:  I love my parents, Lady Gaga and Humpty Dumpty.

With the Oxford comma:  I love my parents, Lady Gaga, and Humpty Dumpty.