Lean UX has its roots in agile-development and caters user experience engineering design to the flexible and iterative work approach of agile development.
Lean UX is the practice of bringing the true nature of our work to light faster, with less emphasis on deliverables and greater focus on the actual experience being designed.
Lean UX is considered to be orientated more towards business and development needs than delivering a full scale user experience design and its results. In a short cycled and iterative workflow, implementations require quick UX solutions to specific problems at hand.
- http://www.andersramsay.com/2012/04/24/agile-ux-vs-lean-ux/ - article comparing agile and lean UX to "traditional" UX approaches
- http://luxr.co/10_principles_of_lean_user_experience - article on lean UX approaches