Recursion

Recursion, as it applies to PHP, refers to a function that calls itself to solve a problem. A recursive function distinguishes itself by solving small parts of the problem until it resolves the main issue. Think of it as breaking down a task into smaller tasks that are easier to solve. However, careful design is needed to ensure the recursive function has a clear stopping point, or else it can result in an infinite loop. Here's a quick example of a simple recursive function in PHP:

function countDown($count) {
    echo $count;
    if($count > 0) {
        countDown($count - 1);
    }
}
countDown(5);

In this example, the function countDown calls itself until the count hits zero, displaying numbers from 5 to 0.