Pink Noise

[Dionysus]

Pink Noise is much akin to "White Noise" whereas it contains all frequencies in the audible spectrum (technically it contains ALL frequencies, but normally further filtering removes the frequencies below 20hz and above 20khz for the sake of not damaging loudspeakers). However the distribution of energy is even across the frequencies, unlike white noise.
Pink noise is commonly used as a diagnostic aid in audio systems. It is a much more realistic signal to use than White Noise since music has much more energy in the low-end than the high-end.
It is important to avoid sending audio energy at frequencies outside of the range of your loudspeakers as this can damage them.

Pink Noise is white noise that has been modified with a pinking filter (really). Such a filter is nothing more than a 3 dB per octave roll-off that commences at a sub-audio frequency and continues to reduce the level as the frequency goes higher and higher. In essence, it nullifies the 3dB per octave rise in energy of the white noise signal to create noise which as equal energy per octave.
Since pink noise has equal energy per octave, it is more useful as a loud-speaker test and calibration signal...