"The Echo of Thunder" refers to the sound phenomenon that occurs when thunder reverberates off surfaces, creating a delayed and repeated sound. This effect happens when lightning strikes, producing a loud clap of thunder that can bounce off mountains, buildings, or other obstacles, causing the sound to linger in the air. The phenomenon is influenced by factors such as distance, terrain, and atmospheric conditions. The speed of sound is approximately 343 meters per second, so the time between seeing lightning and hearing thunder can help estimate how far away the storm is, a principle often summarized by the flash-to-bang method.