A character or point (,) marking the smallest divisions of a sentence, written or printed.
2.
(Mus.) A small interval (the difference between a major and minor half step), seldom used except by tuners.
Comma bacillus (Physiol.), a variety of bacillus shaped like a comma, found in the intestines of patients suffering from cholera. It is considered by some as having a special relation to the disease; called also cholera bacillus.
Comma butterfly (Zool.), an American butterfly (Grapta comma), having a white comma-shaped marking on the under side of the wings.
... the domestic silver. We like things new and primarily our own. We have a wholesome instinct against infection, except, it seems, in the matter of ideas. An authorling will deliberately inoculate his copy with the inverted comma bacillus, till the page swims unsteadily, counting the fever a glow of pure literary healthiness. Yet this reproduction, rightly considered, is merely a proof that his appetite for books has run beyond his digestion. Or his industry may be to seek. You expect ... — Certain Personal Matters • H. G. Wells