The Minotaur Horn is a quest item dropped by the Minotaur while the player is on the quest "The Mighty Horn".
There is a bug on the in-game stats page, however. As seen in the image to the right, the name of the item is not Minotaur Horn, as it is referred to in-game, but "Mintoaur Horn". This is likely a typo and not intentional.