The Frost Bow is a special bow of FrostCraft. It fires frozen-tip arrows that freeze mobs and players on hit. it applies the Freeze and FrostBurn effect to the mob/player it hits. If you get an flame enchantment on a Frost Bow then the bow will show this line in it's description:
"What a waste of a Frost Bow"
This means that it is unable to freeze and frostburn mobs on hit.