A comma is a punctuation mark that represents a short pause and is used to divide parts of a sentence. It has the same shape as an apostrophe or single closing quotation mark in many typefaces, but it differs from them in being placed on the baseline of the text. The word "comma" comes from the Greek κόμμα (kómma), which originally meant a cut-off piece, specifically in grammar, a short clause.
Commas have many different uses in English, including separating items in a list of three or more, connecting two independent clauses with a coordinating conjunction, setting apart non-restrictive relative clauses, setting apart nonessential appositives, setting apart introductory phrases, setting apart interrupters and parenthetical elements, setting apart question tags, setting apart names in direct address, and separating parts of a date. Commas are often the cause of many grammatical mistakes, and there are many rules regarding their usage.
