A Closure is essentially the same as a Lambda apart from it can access variables outside the scope that it was created.

For example:
<?php
 $user = "PHPCodez";
 // Create a Closure 
 $greeting = function() use ($user) { 
 echo "Hello $user"; 
 };

$greeting();

As you can see above, the Closure is able to access the $user variable. because it was declared in the use clause of the Closure function definition.

If you were to alter the $user variable within the Closure, it would not effect the original variable. To update the original variable, we can append an ampersand. An ampersand before a variable means this is a reference and so the original variable is also updated.

Closures are also useful when using PHP functions that accept a callback function like array_map, array_filter, array_reduce or array_walk.

The array_walk function takes an array and runs it through the callback function.

Again, you can access variables outside the scope of the Closure by using the use clause:

In the example above, it probably wouldn’t make sense to create a function to just multiply two numbers together. If you were to create function to do a job like this, then come back to the code a while later you will probably be thinking why did you bother create a globally accessible function only to be used once? By using a Closure as the callback, we can use the function once and then forget about it.