Lean startup is an approach to new product development that aims to shorten product development cycles through a build-measure-learn feedback loop. It emphasizes rapid experimentation through developing minimum viable products to test core hypotheses and customer feedback, and pivoting if needed based on learnings rather than committing large sums to an unknown outcome. The goal is to reduce wasted effort on products that customers do not want and build products they love through iterative releases and customer-centric development.