Kage Bunshin no Jutsu is Naruto's 'speciality' move and was the first, and only move he learnt from the scroll of sealing he stole from Konoha village in the first episode. Unlike Bunshin no jutsu which creates copies that are merely illusions Kage Bunshin no jutsu creates solid copies, capable of doing damage but which dissapear after taking a direct hit. Naruto uses his Kage Bunshin for a variety of uses, such as diversions, attacks and performing rasengan.
Naruto's "Naruto Rendan" uses his Kage Bunshin no jutsu
Kage bunshin no jutsu is a shadow replication technique from the anime series Naruto. "Shadow" has little to do with shadows themselves, but rather refer to a type of jutsus known as shadow jutsus, or kage jutsus if you will. Whereas a normal replication technique would create a near perfect copy of the one performing the teqhnique, the shadow replication is far superior in that it can create a vast number of replications while not using proportionally more chakra.
kage bunshin no jutsu is naruto's worst -and- best fighting move. He always hated the replication techniques at school because he was so bad at them, but then again kage bunshin no jutsu is so powerful that it enables him to easily create a horde of replications rather easily.