http://culttt.com/2013/03/25/what-are-php-lambdas-and-closures/
What is a Lambda?
A Lambda is an anonymous function that is can be assigned to a variable or passed to another function as an argument. Because the function has no name, you can’t call it like a regular function. Instead you must either assign it to a variable or pass it to another function as an argument.
Lambdas are useful because they are throw away functions that you can use once. Often, you will need a function to do a job, but it doesn’t make sense to have it within the global scope or to even make it available as part of your code. Instead of having a function used once and then left lying around, you can use a Lambda instead.
What is a closure ?
A Closure is essentially the same as a Lambda apart from it can access variables outside the scope that it was created.
// Create a user
$user = "Philip";
// Create a Closure
$greeting = function() use ($user) {
echo "Hello $user";
};
// Greet the user
$greeting(); // Returns "Hello Philip"
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.