white noise

Short definition from Wiktionary

Noun

1. 1
   A random signal (or process) with a flat power spectral density; a signal with a power spectral density that has equal power in any band, at any centre frequency, having a given bandwidth.
2. 2
   Any nondescript noise used for background or to mask or drown out other noise.
3. 3
   Speech that goes ignored or uncomprehended.