For further information on this race, refer to Namekian.
Namek is a planet which is the original home of the Namekian race. In Dragonball Z, it is a planet of Vital importance.
Firstly, the planet has Dragonballs, which, unlike those on Earth, will grant you 3 wishes. This is the reason Freeza, Vegita, and Bulma krillen and Gohan go to the planet.