Closures

A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). In other words, a closure gives you access to an outer function’s scope from an inner function. In JavaScript, closures are created every time a function is created, at function creation time.

— MDN Web Docs

function greetings() {
  var name = "Hello World!"; // name is a local variable created by greetings.

  function displayGreetings() {
    // displayGreetings() is the inner function, that forms the closure.
    console.log(name); // use variable declared in the parent function
  }
  displayGreetings();
}
greetings();