Lean startup is practiced widely in silicon valley, China, and most of the successful startups.
According to wikipedia, Lean startup is a methodology for developing businesses and products that aims to shorten product development cycles and rapidly discover if a proposed business model is viable; this is achieved by adopting a combination of business-hypothesis-driven experimentation, iterative product releases, and validated learning.
In short, it's a data-driven mindset in building a business/startup.
Continuously do as many experiments as possible using cheapest & most rapid methods, in order to improve startup scalability.
This approach is able to help startups to scale rapidly and Venture Capitals love this approach.
Not only for startups, this mindset can be applied in conventional businesses too. Simply because we are living in a world where data is king.