The furlong is an old English unit of distance that is still regularly used in horse racing. A furlong is 660 feet, which is one-eighth of a mile.
Originally a furlong represented the distance that a team of oxen could plough a furrow (a long shallow trench in a field), on average, before they had to rest. This was also the length of an acre, which in Anglo-Saxon times was considered to be 40 × 4 rods (660 × 66 feet). A furlong appears to have been used as a horse racing measurement because in early days racing took place in fields next to ground that had been ploughed. Therefore, the distance could be assessed quickly by comparing the racetrack with the number of furrows made in the neighbouring ploughed field.