Everytime I go to a conference here in Berlin I hear the term Lean. Sometimes I just think people use it to make their work more believable or modern. The term basically means "removing waste" and is something that came from the automobile industry. You could really put this definition in any sentence and It will actually make that world sound really professional: lean constructor, lean lover, lean superhero.  I would say: stop using it! but then you won't sound cool and professional, I can not argue against that.

There are of course concepts that are more developed. I have found at the moment three: lean thinking, lean manufacturing and lean development. All have a set of principles to follow. I'll put this here but if you want more information just google it! There is so much information that I don't want to repeat it again.

Lean Thinking

Principles:  
    Specify Value as perceived by the Customer
    Identify the Value Stream
    Make the Value Flow through the Value Stream.
    Pull the Value from the Value Stream
    Strive for Perfection.

Lean  Manufacturing

Principles:
    Over Production
    Waste of Unnecessary Motion
    Waste of Inventory
    Production of Defects
    Waste of Waiting
    Waste of Transportation
    Waste of Overprocessing

Lean Development

Principles:
    Eliminate waste
    Amplify learning
    Decide as late as possible
    Deliver as fast as possible
    Empower the team
    Build integrity in
    See the whole