Recessed Lighting has always been composed of 3 elements- the can (the actual fixture that is hardwired and holds the light source), the baffle (this surrounds the light source and projects the light outward while minimizing glare) and the trim ring (this covers up the slightly larger hole cut by the electrician that allows the light into the room as well as creates a barrier between the air-conditioned space and the unairconditioned air from the plenum above).
New Trimless Recessed lights omit the trim ring and offer a much cleaner look. The issue with these is only one of acceptance. The process for Contractors involves scheduling of the Drywall finishers after the Electricians are done installing. Then, the drywall crew mud and sand over the invisible trim frame before the Electrician snaps in the baffle and, voila, a much needed evolution of recessed lighting made easier through LED technology.