The Elder Scrolls III: Bloodmoon is an expansion pack for The Elder Scrolls III: Morrowind.

A quote from Bethesda Softworks:

Your journey north from Vvardenfell by ship will bring you to a whole new world, where the ashlands and rainy coasts of Morrowind give way to forests and hills covered with snow and ice. In the huge wilderness of Solstheim you'll experience snow, blizzards, and new creatures, including frost trolls, ice minions, and wolves…just to name a few.