Unicum
A player in the top few percent of the server, named for the purple band their rating colour falls into.
Also known as unicums, purple player, super unicum, purple.
Unicum is Latin for something unique, and the community borrowed it for the players whose rating lands in the purple range, roughly the best five percent of accounts. Super unicum is the darker purple above it, the top one percent or so.
It is a statistical label rather than a title. Nothing in the game awards it, no interface displays it, and the exact threshold depends on which rating is being quoted, but the colour is universally understood: purple means the account performs far above the server.
The word carries some baggage. It is used as a compliment, as a self-description and, often enough, as an accusation of taking the game too seriously.