These are sometimes confused, especially by the wrong use of i.e. to introduce an example. i.e. ( id est) means "that is" and introduces a definition, as one might say "we are meeting on the second Tuesday of this month, i.e. the tenth". E.g. (exempli gratia) means "for the sake of example" and introduces an illustration, as one might say "let us meet on a fixed day every month, e.g. the second Tuesday".