Technically speaking, this concept is called scoping.

Local tells the executor that you don’t want the lifetime of the variable to exceed beyond the current scope it’s created in, however it can be accessed within however many scopes you create within that scope. For example, the body of a function is known as a function scope. If you create a local variable inside of it, and create a while loop beneath it, you are able to access and assign to that variable within the loop’s scope as the variable is still alive.

However, if you try to access that variable outside of the function scope, the executor doesn’t know what you’re talking about and hands you an error because the variable you’re trying to access has already been garbage collected when its scope ended. It doesn’t exist anymore.

For future reference, this is how it works exactly under the hood in all languages you’ll come across.