In PHP, the term "closure" refers to an anonymous function that can retain and use external variables even after the context in which they were created has already terminated. Closures are used to create functions that can access variables from the scope in which they were defined, even after that scope is no longer active.
Here's an example of a simple closure in PHP:
<?php
$greet = function($name) {
echo "Hello, $name!";
};
$greet('World');
?>
In this example, `$greet` is a closure that takes the $name argument and outputs a greeting message. You can pass a value to the argument and invoke the closure just like a regular function.
Closures are particularly useful when working with higher-order functions, such as `array_map`, `array_filter`, or `usort`, where you may need to pass a function as an argument. Closures allow you to create anonymous functions on the fly, providing convenience in various programming scenarios.
