White noise is a random signal with a flat power spectral density. In other words, the signal's power spectral density has equal power in any band, at any centre frequency, having a given bandwidth. White noise is considered analogous to white light which contains all frequencies.
At SimplyNoise you can use a slider to find a comfort zone and enjoy the auditory zen. The site claims you can use it for aid sleep, to block distractions, mask Tinnitus, configure audio equipment, and sooth migrains.