How can you explain JavaScript closure to a beginner?

Closure can be explained as scope that is still alive when the parent function execution has finished, because it returned another function that might use variables from the parent function's scope later.

Ex.

function add (a) {
  return function (b) {
    return a + b;
  }
}

let addFive = add(5),
  addSeven = add(7);

console.log(addFive(10)); //15
console.log(addSeven(9)); //16

So here in addFive(10) ,  the variable a of parent function is alive because it returns a function that uses a.