the use of a comma, rather than a semicolon, colon, or period, to separate related main clauses in the absence of a coordinating conjunction: often considered to be incorrect or undesirable, especially in formal writing.
a comma used after the next-to-last item in a series of three or more items when the next-to-last and last items are separated by a conjunction. In the series A, B, C, or D, the comma after C is the series comma.
