Über is a German word that means above or over. In the 2000s it has migrated into the English language and is often spelled uber, rather than featuring the umlaut above the "u". It is often used as a prefix in English to describe something above and beyond the unusual, and is quite commonly used among teens and young adults.
Most common uses of über in English are in television, film and in the gaming world. The word über shows up frequently in texting and Internet chatting, replacing words of like hyper, rad, and awesome as ways to describe the superior or awesome quality of something being described. It doesn’t always have positive connotations. For example, in the final season of Buffy the Vampire Slayer, one of the goals was to defeat übervamps, extremely tough prehistoric vampires that populated the Hellmouth.
A terrific video gamer may be called an überkid, or über gamer. In some cases, gamers get to über levels in a video game, or may become an über character. Some cheat codes allow a character to become invincible, allowing, as for example in Star Wars Jedi Knight, the opportunity for a character to become an über Jedi.
Though we might be accustomed to thinking of über in regards to modern slang language, the term über in Germany has long been used in much the same way. Friedrich Nietzsche, for instance, predicted the coming of a race of übermensch, or superior men who would overcome the state of simple human being and would reject societal rules and be able to use their minds to overcome the weaker human. Many have considered the Nazis as the übermensch; yet reading Nietzsche reveals this was clearly not his intent. He was speaking in philosophical terms and not discussing superior armed strength and the destruction of the Jewish people.
You could call the term über merely the latest in a series of terms that have been borrowed or completely stolen from Germanic languages. Much of English derives from Germanic origin, and in fact über sounds not very different from our word super to which it is extremely similar. The word easily migrates into English, where modern usage shows it is increasing in popularity. Someday only those with training in German language may recognize the word as anything other than English.