Badass is a slang word that can have many meanings depending on the context. For example, if you say he is a badass fighter that means that he is tough, and cool. If you say " That's a badass motorcycle" your saying that you really like the motorcycle. It's basically used to describe something that you like with strong emphasis.

Romella already answered, but FYI it also is used sarcastically. If somebody is acting tough someone might say sarcastically "oh, you're a real bad as aren't you?"