A furlong is a measure of distance within Imperial units and U.S. customary units. Although its definition has varied historically, in modern terms it equals 660 feet or 220 yards, and is therefore equal to 201.168 metres. There are eight furlongs in a mile. The name "furlong" derives from the Old English words furh (furrow) and lang (long). It originally referred to the length of the furrow in one acre of a ploughed open field (a medieval communal field which was divided into strips).
Distances less than a mile for thoroughbred horse races in the United Kingdom, Ireland and the United States are given in furlongs, but the unit is otherwise no longer much used. Its official use was abolished in the United Kingdom under the Weights and Measures Act 1985, which also abolished from official use many other traditional units of measurement.
Coincidentally, since a kilometre is about five-eighths of a mile, it is also about five furlongs.
In The Lord of the Rings by J. R. R. Tolkien, Farmer Maggot's farm is called "Bamfurlong".