White noise
Every value picked on its own at random, like the static on an old television.
See it in Noise & texture. Pick the Film grain preset and look closely at the speckle.
In plain words
In white noise, every value ignores its neighbours. A bright pixel is as likely next to a dark one as next to another bright one. It looks like television static, and it sounds like a steady hiss. The name comes from white light, which mixes every colour equally. Smooth noises are built by blending white noise across space.