TOPIC: Lean principles

I read that with the Jan 2016 updates, Lean Principles is a task and that questions may appear in the PMP exam. However, no where in the PMBOK or the many videos I reviewed online describes Lean Principles at all.

Can someone please help me understand what has been added to the content related to lean principles?

You are correct with one slight correction... "Lean and efficiency principles" are listed as a Knowledge & Skill (not task) in Domain II "Planning".

These principles are not specifically called out, but they are discussed as part of Module 50 of The PM PrepCast where we review Agile, The Agile Manifesto and Scrum. These principles are at the core of both the manifesto and Scrum.