what is a superlens?

Answer 1

It's a lens (like the magnifying glass) that can magnify/view extremely small objects, even smaller than atoms.

Answer 2

It's a special lens that so far has achieved better resolution than a conventional lens, but as yet isn't near the single-atom point. conventional lenses can resolve down to 1/2 wavelength of the light being used, and UC-Berkeley researchers have achieved 1/6 wavelength with a lens comprising a thin film of silver. See the ref.