According to the Norwegian Fjord Horse Registry,
It is an agile breed of light draft horse build. All Fjord horses are dun in color...it has been used for hundreds of years as a farm horse in Norway, and in modern times is popular for its generally good temperament. It is used both as a harness horse and under saddle.And according to horse-genetics.com,
The Norwegian Fjord Horse retains many characteristics of primitive European horses and bears a striking resemblance to the horses painted on cave walls by ice age artists some 30,000 years ago.
Terna, Elisabeth and Oleanna's horse, is their all-purpose farm horse, and a sweet old guy. I just wish I could remember why I named him Terna. :)
Update: Thor Bugge Lanesskog has a wonderfully succinct overview of the fjord horse, along with some excellent photos of the horse in action on a farm!