Comma (diacritic)

The comma ( , ) is a punctuation mark that appears in several variants in various languages. 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. Some typefaces render it as a small line, slightly curved or straight but inclined from the vertical, or with the appearance of a small, filled-in number nine.

The comma is used in many contexts and languages, mainly for separating parts of a sentence such as clauses, and items in lists, particularly when there are three or more items listed. The word comma comes from the Greek (kómma), which originally meant a cut-off piece; specifically, in grammar, a short clause.

A comma-shaped mark is used as a diacritic in several writing systems, and is considered distinct from the cedilla. The rough and smooth breathings (ἁ, ἀ) appear above the letter in Ancient Greek, and the comma diacritic appears below the letter in Latvian, Romanian, and Livonian.

The basic comma is defined in Unicode as U+002C , COMMA (HTML ,), and many variants by typography or language are also defined.

Some languages use a completely different sort of character for the purpose of the comma.

There are also a number of comma-like diacritics with "COMMA" in their Unicode names. These do not serve a punctuation function. A comma-like low quotation mark is also available (shown below; raised single quotation marks are not shown).

...
Wikipedia