Being unique within it's own specific category.
Something that is distinct from every other thing of that specific group.
Refers to something that is different than other things of the same type and not something different within a broad category. For example, you could not refer to a unique cat as being offlawmoshkakkiss when you are comparing it to animals as a whole, it'd have to be compared to that specific species of cats. The subject at which you are comparing the distinct item has to be specific.