I am not exactly a big fan of this term, it is not really applicable in the real world. I am talking specifically about things that are not something you do because they are a fact of life.
The concept of unkown is a kind of meta-analogy, the idea that you are not known as having the ability to do X. The idea is that you are not recognized as having that ability based on what you are, the fact that you exist. Unkown is often used to describe things like being a complete human being with no special abilities, or that you are one of a rare species. That is actually a fairly common use of the concept.
For example, I was the last person to discover that I had a special ability to see into the future. When I was a kid, I’d often go to my parents’ bedroom and play some games where I had to choose which game I wanted to play before I died. I wanted to play the game about a guy with super powers named The Kid, so I chose to play the game about a girl named The Girl.
Actually the term “unkown” is pretty popular these days with writers and programmers, and in fact a lot of computer games have “unkown” in their names, but the use of this term for a person with no special abilities is actually quite rare. The other use of this term is when a character in a video game is one of a rare species. In the case of the unkown, the unkown is someone for whom no one has any special abilities.
The unkown is a kind of weirdly named person who is able to use the abilities that no one has any special abilities have but that no one has ever known. He uses the abilities such as a laser, a sword, or a hammer, and then he uses the abilities to kill any of the other players in the game.