Perhaps a few simpler concepts?

It's a storage. All right. Everyone knows what a storage is. That's a place where you can store data. And read it later, if and when it's still available.

It's a local storage. All right. That means that the storage is not universally (globally) available. It is bound to something local.

Now what is that something?

Local storage like thread-local in threaded programming except there's no threaded programming. (“A samurai without a sword is like a samurai with one, but only without one”.)

Сlosures are wrapped around portions of a continuation chain taking the place of mutable cells bound to thread data structures. (Really needs explaining. What is that “continuation chain”, what are “mutable cells”, what are “thread data structures” in Node's JavaScript?)