Accessible (as applied to wiring methods). Capable of being removed or exposed without damaging the building structure or finish or not permanently closed in by the structure or finish of the building.
If you remove the insulation, a ceiling tile or access panel you are "exsposing" it without damage to the structure "this would be the framing" or the finish which could be a number of things such as sheet rock panelling, ceramic tile etc.
314.29 Boxes, Conduit Bodies, and Handhole Enclosures to Be Accessible. Boxes, conduit bodies, and hand-hole enclosures shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or, in underground circuits, without excavating sidewalks, paving, earth, or other substance that is to be used to establish the finished grade.
Exception: Listed boxes and hand-whole enclosures shall be permitted where covered by gravel, light aggregate, or non-cohesive granulated soil if their location is effectively identified and accessible, for excavation.
This exception would equate to the same action as removing the insulation.