In the natural world, there are many physical processes which produce noise with what is known as a "pink" distribution of power. "Pink" noise has an even distribution of power if the frequency is mapped in a logarithmic scale. A straightforward example would be that there is as much noise power in the octave 200 to 400 Hz as there is in the octave 2,000 to 4,000 Hz. Consequently, it seems, our ears tell us that this is a "natural" even noise.
"power" means the average power or energy contained in a signal over a long period of time.
Pink noise has the same distribution of power for each octave, so the power between 0.5 Hz and 1 Hz is the same as between 5,000 Hz and 10,000 Hz.
Since power is proportional to amplitude squared, the energy per Hz will decline at higher frequencies at the rate of about -3dB per octave. To be absolutely precise, the rolloff should be -10dB/decade, which is about 3.0102999 dB/octave.
The most obvious use of pink noise is as an audio signal, to be used directly, to be filtered or to be used to modulate something.
Now how does that grab ya