Although some authorities argue that its meaning has expanded in recent years, strictly speaking, this word only means one thing:
1. being the only one of its kind; unlike anything else.
Therefore, something cannot be qualified as being "one of the most unique," or "very unique," or anything else as is the common usage in many television commercials and academic essays. It's just "unique" that's it -- and it has to be a truly one-of-a-kind item (such as a fingerprint, a mineral specimen, or this post), or a collection of such items:
"The professor has a unique collection of crystals that he gathered from all over the world."
On the other hand, the word can also be used thusly at parties:
Question: "How do you catch a unique bird?"
Answer: "Unique up behind it." hahaha