A super-Earth is a planet which has a higher mass (often with a larger size but not as large as a gas giant) than our planet. The name super-Earth implies a world like ours, but this is misleading as the planet may actually be gaseous or a gas-dwarf. As these are small, dark objects (compared to a star that is) at a great distance from us they are not easy to spot and usually get picked up from Space-borne telescopes that do not have to look through the atmosphere.
The first super-Earth discovered by humanity was in 1992, found to be orbiting a pulsar called B1257+12 and is around 1000 light years away. The nearest super-Earth known is orbiting the red dwarf Gilese 876 at 15 light years away and nips around its star in only two sidereal (this, Earth) days.