The popular definition of a “straight line” as “the shortest distance between two points” is one of the few pieces of mathematical jargon in general circulation in the English language. This is unfortunate, for it is not a good definition, and one may well wonder who originated it. Euclid is not to blame, for he defined a straight line as “that which lies evenly between its points”. (This is indeed cryptic, and Sir Thomas Heath, in a lengthy analysis of the original Greek, had to confess that “the language is...hopelessly obscure”.)