Brown noise is a type of sound signal that contains a lower frequency range compared to other noise types, such as white noise. It is characterized by a deeper, richer sound, similar to the sound of a distant waterfall or thunder. The name "brown noise" comes from the Brownian motion, which describes the random movement of particles in a fluid. Many people use brown noise for relaxation or sleep, as it can help mask other disruptive sounds. It is often found in sound machines and apps designed to promote a calming environment. Some studies suggest that brown noise may aid concentration and improve focus for certain tasks.