Dictionary.com
definitions

pink noise

noun
  1. a random signal within the audible frequency range whose amplitude decreases as frequency increases, maintaining constant audio power per frequency increment.

Origin of pink noise

First recorded in 1960–65
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for pink noise

pink noise

noun
  1. noise containing a mixture of frequencies, but excluding higher frequencies
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012