The kilometre is a unit of length and is a multiple of the metre; an SI derived unit. It has the symbol km.
A kilometre is equal to 1000m, 1094 yards and 0.621 miles.
Kilometres is used to measure road distances in the US, though the UK is still using the imperial "sister" miles.
The furlong is a unit of length in the imperial unit system and uses the symbol fur.
One furlong is equal to 1/8 mile, 660 feet, 220 yards, 40 rods, 10 chains or ≈ 201m.
The furlong was a term used to describe the legnth of a furrow in one acre of a ploughed open field (communal field). It now only really remains in the world of horse-racing in UK, Ireland, Canada and the US.