Lean is an expression given to any noun which is pure, trustworthy and generally not full of shit.
Derived from the term to describe a non-fatty piece of steak, lean can be extended to describe a person for example. "That guy is lean bro", meaning he is not full of shit and he is a cool guy.
An important feature of this definition is that one cannot claim lean upon themselves. One cannot say that their own stuff is lean, or that they are lean them-self. Lean can only be given, bestowed or honored to a person, place or thing... ya hear me?