Lean UX is a combination of Lean Startup, Agile and UX methodologies that aims to shorten product development cycles and increase success rates. It advocates for building digital products through small, iterative releases rather than big bang launches. This allows teams to validate assumptions and hypotheses with customers early to learn quickly and reduce risks. Key Lean UX practices include lightweight personas, rapid prototyping, customer conversations, collaboration across teams, and validated learning through experimentation and data collection.