The Oxford comma, or serial comma, is a comma inserted in a list before the final 'and' or 'or':
'Apples, oranges, bananas, and pears' has a serial comma. 'Apples, oranges, bananas and pears' does not.
It can seem like one of those punctuation pedantries which does not matter in real life, but it's recently appeared in a court case in the USA. There's a law in Maine which states that if work connected with perishable food takes extra time, overtime is not payable. Presumably this is because the work cannot be delayed until the next day and employers need certainty over costs.
A dairy has been successfully sued by its drivers because of the lack of a serial comma in the following statement. The exemption to the overtime rules, according to the Maine law, applies to:
The intention appears to have been that 'shipment or distribution' represented two items in the list: that is 'packing for shipment' and 'distribution' are separate activities and both are ineligible for overtime payments.
The drivers contended, though, that it was a single item 'packing for shipment or distribution', and therefore that it was 'packing' that was exempt from overtime, not distribution (which is what drivers do).
The appeal court agreed with the drivers and you can read the judgement here: http://media.ca1.uscourts.gov/pdf.opinions/16-1901P-01A.pdf
The story was covered in the Guardian and other newspapers. And there's a nice commentary here from David Marsh, giving both sides of the argument and some classic examples.
What's not clear to me is how long this law has been operation, and what the practice has actually been up to now - has overtime never been paid, but a clever lawyer has spotted the absence of a comma? Or is this a new thing and the drivers genuinely thought their understanding was shared by the drafters of the statute?
The problem with punctuation (and why, it is sometimes suggested, lawyers traditionally don't like it) is that an awful lot hangs on a small smudge on the page. So how about a more graphic solution. This is what the drivers thought it meant:
This is what the employers thought:
Another argument for visualisation in legal drafting.