Currying is a technique of transforming a function that takes multiple arguments to a chain of functions where each function will take exactly one argument. In other words, if a function can be written as f(x,y,z), then the currying version of this will be f(x)(y)(z). let's consider the following example:

function sum($a, $b, $c) {
    return $a + $b + $c;
}

Here, we have written a simple function with three parameters and when called with numbers, it will return sum of the numbers. Now, if we write this function as a curry, it will look like this:

function currySum($a) { 
    return function($b) use ($a) { 
        return function ($c) use ($a, $b) { 
            return $a + $b + $c; 
        }; 
    }; 
} 

$sum = currySum(10)(20)(30); 

echo $sum;

Now if we run the currySum as a currying function, we will get the result 60 for the preceding example. This is a very useful feature for functional programming.