late 16th century (originally as a term in rhetoric denoting a group of words shorter than a colon; see colon1): via Latin from Greek komma 'piece cut off, short clause', from koptein 'cut'
This punctuation mark has the following uses: to separate the items in a list:...tens of thousands of them: Christians, Hindus, Muslims, Sikhs. to place a section of a sentence in parenthesis (as brackets do):Bill the dog, happy as ever to be out and about, was sniffing everything in sight. to mark the divisions between the clauses in a complex sentence:These weedkillers may, if used on new lawns, damage young seedling grasses before they are well established. to separate sections of a sentence to make it easier to read:To make a hot compress, pour hot water into a bowl and then add the essential oil. to introduce and/or end a piece of direct speech:‘No, sir,’ said Stephen, ‘and that is what is so curious.’ You do not need to use a comma between nouns that are in apposition:my wife Dorothy Alison and her friend Beth were attracted to the same man at a party. Commas should be used to surround a noun that is in parenthesis:Pete, his son, cleaned the garden aviary. Use a comma when writing a number that is made up of four or more figures:23,500 1,500 miles but not in dates:1 May 2004 the 1970s