According to the Encyclopaedia Britannica, a furlong is an old English unit of length. The term is, in fact, derived from the old English words ‘fuhr’, meaning ‘furrow’, and ‘lang’, meaning ‘long’; in the traditional medieval farming system in England, known as the ‘open-field’ system, each ploughed furrow ran the length of an acre. The furlong was standardised to 660 feet or 220 yards – that is, one-eighth of a mile – in the late thirteenth or early fourteenth century and has been the traditional unit of measurement for British horse races since the first formal race meetings in the sixteenth century.
The furlong remained an official measurement until the Eighties but, today, is used almost exclusively in horse racing; indeed, to the layman, the furlong is probably the distance most associated with the sport. That said, aside from the fact that British racecourses are geared up to use furlongs, in terms of marker posts and the like, there is no real reason why race distances cannot be measured in metres, as they are elsewhere in Europe. However, the British racing industry is notoriously traditional and tests of distance markers in furlongs and metres have received, at best, a lukewarm reception.