New Namek (Shin Namekkusei) is the new home of the Namekian race. It is similar to the original Namek, because of the green water, green sky and blue grass.
Following the destruction of the original Namek by Frieza, the revived Namekians were forced to spend an entire year on Earth inside the Capsule Corporation compound with Bulma and the Briefs. Eventually, King Kai discovered a planet with an atmosphere almost identical to Namek, and thus the Namekians were wished to that planet after bidding farewell to their friends from Earth.
New Namek is mentioned and seen in the Cell Games Saga, Dragon Ball Z: The Return of Cooler, the Kid Buu Saga, and Baby Saga. During the Cell Games Saga, Goku travels to New Namek using Instant Transmission in order to find a replacement Guardian for Earth. Dende is selected, and happily accompanies Goku back to Earth.
In The Return of Cooler, Cooler attempts to use New Namek as fuel for the Big Gete Star. Goku and some of the other Z Fighters battle Cooler, his Cyclopian Guards, and his Meta-Coolers on New Namek.
Later in the series, Goku asks for the use of the Namekians' help to combat foes like Kid Buu and Baby.