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Comma (punctuation)

A comma is a punctuation mark, written

Some typefaces render it as a small line, slightly curved or straight, some like a small filled-in number 9. It is used in many contexts, principally for separating things. According to the Oxford English Dictionary, "comma" comes directly from the Greek komma, which means "something cut off" or "a short clause".

Table of contents
1 Grammar
2 Numbers
3 Diacritic
4 Computer programming


It is used to mark off separate elements in a sentence, introductory clauses, words in a series, parenthetical phrases, or interjections.

Commas are also used to separate items in lists, and to present large numbers in a more readable form.

These formal uses frequently also indicate a pause in speech. Writers often use optional commas for stylistic reasons, to indicate such a pause where none may be required, grammatically.

Fowler's Modern English Usage demonstrates this optional use of commas with two sentences, differing only by a comma:

The use of a comma before the word "and" in a list of more than two things is called the Oxford comma:

"We had tea, biscuits, and cake."

It is so named because its usage is recommended in the style guide of the Oxford University Press.


In many European languages, commas are used as decimal points. Thus, "1,5 V" means "one and one-half volts". However, commas are never used this way in English, except in South Africa. When using commas in a number in English, the commas are placed before every third digit, starting from the right. Thus, the number fifteen million can be written as "15,000,000". A number with a decimal does not use commas in the fractional portion. Thus, "twelve thousand fifty-one dollars and seven centss" is written in symbols as "$12,051.07". In South Africa, the comma is replaced with a space, and the decimal point by a comma so that the amount would be written "$12 051,07." In South African English, 99,9% would therefore be read as "ninety-nine comma nine per cent."


As a diacritic mark, comma is used in Romanian under s: Ș (ș), and under t: Ț (ț).

Some consider the diacritics on the Latvian consonants g, k, l, n, and formerly r to be commas as well. While their Adobe glyph names are commas, Unicode named them cedillas.

Computer programming

In computer programming, the comma corresponds to Unicode and ASCII character 44, or 0x002C.

In the C programming language, "," is an operator which evaluates its first argument (which presumably has side-effects) and then returns the value of its second argument. This is useful in "for" statements and macros.

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