An Extrasolar planet is a planet outside of the Solar System. Around 1,800 of these planets have been discovered (1,876 as of January 9th 2015). The Kepler mission to discover earth-like planets have discovered around 262 habitable planets which might harbor life. In the Milky Way Galaxy alone, there is an estimation to be around 400 billion planets.
The closest star to us that may have an Extrasolar planet is Alpha Centauri, and its planet Alpha Centauri Bb which is located approximately 4.3 light years away from Earth, though the planet's existence has been disputed.