What is pain-free?

To be in a state of not feeling overt pain. A state of anti-inflammation.

The name for a Schiff brand (trademark) joint supplement that was later pulled by the FDA - as it was too blatantly a health claim in the name of the product, later renamed.

In common useage now, the term can indicate any mode of feeling good or feeling a lack of pain ... be it physical, mental, emotional, etc.