What "cream" means
When concrete is placed and trowelled, the fine paste, cement and the finest sand, rises to the top and forms a layer a couple of millimetres thick. Polishing at the cream level means running a diamond grit progression that refines that layer to a sheen without cutting through it. Nothing aggregate-sized is exposed, so the floor stays a soft, continuous, cloudy grey with no speckle. It is the closest polished concrete gets to looking like a poured stone surface rather than a terrazzo.
The forgiving option
Exposing sand or stone requires cutting down to a consistent depth across the whole floor, which means a slab that is not flat gets cut deeper in the high spots than the low ones, producing visible variation in how much aggregate shows. That is the single most common disappointment in polished concrete. Cream polish avoids the problem entirely by never cutting deep enough for it to matter, which is why on an existing residential slab of unknown flatness it is usually the honest recommendation.
How it is hardened
Polishing without densifying produces a floor that looks finished and dusts within a year. A lithium silicate densifier is applied partway through the grit progression, reacting with free lime in the concrete to fill the pore structure and harden the surface chemically. That is what makes a polished slab abrasion-resistant, and it is why polished concrete has no film to peel: the performance is in the slab, not on it.