An "Echo" is a sound that is reflected off a surface and heard again. It occurs when sound waves bounce back after hitting a barrier, such as a wall or a mountain. This phenomenon can be experienced in various environments, like canyons or empty rooms, where the sound can travel and return to the listener. Echoes are often used in different fields, including acoustics, music, and sonar technology. In music, echoes can create interesting effects, while in sonar, they help locate objects underwater by analyzing the time it takes for sound waves to return.