戻り値

A function can pass a value using an argument when it is called, but as a result of processing in the function, it can return a value from the function to the caller this time.
For example, functions that perform numerical calculations can return the calculation results to the caller, and functions that process strings can return the processed results.

Use the return statement to return a value from a function.

function mul($num1, $num2){
	$sum = $num1 * $num2;
	return $sum;
}

$sum = mul(10, 9);
print "乗算の結果は". $sum . "です。<br>";

print "乗算2の結果は". mul(7, 14)."です。";

乗算の結果は90です。
乗算2の結果は98です。

なるほど、returnで返しているのが戻り値と言えそうですね。