Discuss closures in JavaScript and provide an example of their usage.

Closures are a powerful and fundamental concept in JavaScript that play a significant role in enabling advanced programming patterns. Understanding closures is crucial for writing clean, efficient, and modular code. In JavaScript, a closure is created when a function is defined inside another function and has access to its parent function's variables, even after the parent function has finished executing. The inner function "closes over" the variables of its outer function, forming a closure. This means that the inner function retains access to the variables, parameters, and even the scope chain of its outer function, even when the outer function has completed. Closures are often used to create private variables and functions, encapsulate data, and maintain state within a function. Here's an example to illustrate the concept ....