Lean UX is the newest buzz word in User Experience (UX) Design. Many people use it interchangeably with Agile UX and also define it differently. It appears that there’s also some turf war where people are trying to own the definition. I subscribe to the original lean definition which makes it simply the process of mitigating risks in the assumptions being made for the product or solution being built. Everything else like prototyping, validation, user interviews etc are just the means to do that.
I came across this handy chart by Anders Ramsay that calls out the differences.