What is the definition of Retention Sounds?

Retention sounds, my friend, are like the echo of a forgotten lullaby that refuses to let go, stubbornly refusing to fade away even in the most modern of environments. Imagine this: "The old, dusty library retained the sounds of 90s grunge, making it impossible to focus on a new novel, even though the last time I heard a guitar riff was a decade ago." Now, that's retention sounds at its finest—or its worst.