COMMA , originally, in Greek rhetoric, a short clause, something less than the "colon"; hence a mark , in punctuation, to show the smallest break in the construction of a sentence. The mark is also used to separate numerals, mathematical symbols and the like. Inverted commas, or "quotation-marks," i.e. pairs of commas, the first inverted, and the last upright, are placed at the beginning and end of a sentence or word quoted, or of a word used in a technical or conventional sense; single commas are similarly used for quotations within quotations. The word is also applied to comma-shaped objects, such as the "comma-bacillus," the causal agent in cholera.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)