serial comma
Definition - A [controversial!] comma that some writers place before the conjunction that precedes the last item in a list.
The following usage guides recommend its use:
(1) The Chicago Manual of Style,
(2) Strunk and White's Elements of Style,
(3) the Oxford University Press, and
(4) Fowler's Modern English Usage
However, many newspaper style guides — for example, those published by the New York Times, the Associated Press, The Times of London, and the Canadian Press — recommend that you omit it.

Example -

(1) Lock, stock, and tomahawk
(Note the serial comma before the and.)
(2) My favourite sandwiches are pastrami, ham, cream cheese and jam and peanut butter.
(Note the missing serial comma: looks wrong, tons of ambiguity. This is why I use it.)

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