Mountain REFRAIN is a term used to describe the sound of an ECHO, which is created when a sound is reflected off a surface such as a mountain. The term is derived from the word 'REFRAIN, ' which means to repeat something. An ECHO is created when a sound is repeated multiple times, usually in a rhythmic pattern. This phenomenon can be heard in nature, such as when a person shouts in a canyon or valley and the sound is reflected back. Mountain REFRAIN is also used to describe the sound of music that is repeated in a cyclical pattern.