A reverberation is an echoing sound. When you bang on a big piece of metal, you can hear the reverberation even after you stop banging.
The repeating, often low, booming sound that follows the strum of an electric guitar or the thump of a drumstick on a cymbal is called reverberation. It's frequently described as sound that lingers beyond the original noise. You can also use the word to describe something else that lingers, like a feeling or an effect: "The reverberations of the war lasted for decades." Originally, reverberation was "reflection of light or heat," from the Old French reverberacion, "great flash of light."