The Northern bow is a type of wooden composite bow typical especially for the northern cultures of the UnReal World.
Arguably one of the best bows in the UnReal World. It is as powerful as a longbow but much less accurate, so if you are fighting at mid-range you will quickly see why it is such a popular choice of weapon.
A masterwork Northern bow and superior arrows will make you an incredibly powerful opponent, at a lower weight than carrying a longbow. It is usually found among the Owl people.
URW Game Encyclopedia description
The official URW in-game encyclopedia (accessed by the key) describes the Northern bow thusly:
A composite bow with a set-back handle, covered with birch bark. The northern bow is one of the strongest bows used in the UnReal World; it is nearly as strong as the crossbows used by the foreign soldiers.
In-game encyclopedia entry on the Northern bow