Dual native ISO

An ordinary sensor has one native ISO where the image is cleanest, and everything above it is amplification that drags noise along. A dual native design adds a second circuit that engages higher up the range, so a camera might be clean at ISO 800 and clean again at 4000, with the noisiest results in the gap between the two. That changes how you pick an ISO in low light, because going as low as possible stops being the right answer. Manufacturers publish both values.