die

The code is checking if the value 10 is numeric using the is_numeric() function. If the value is not numeric, the script calls the die() function and prints the string 'This is not a number' and exits the script. If the value is numeric, the script continues to execute the code that follows this block.

The is_numeric() function is used to check if a variable is a number or a numeric string. It returns true if the variable is numeric, otherwise, it returns false. In this case, the variable is a number, so the function returns true, and the code inside the if statement will not execute.

die() function is similar to the exit() function in that it terminates the execution of the script. However, die() also sends a message to the browser. The message parameter is optional, but when provided it is used as the error message. In this case, the message 'This is not a number' is displayed to the browser.

<?php
// You can also trigger or display your own error by using one of the built in functions
// such as die()

// if number 10 is not a number, it will throw an error
if (!is_numeric(10)) {
    die('This is not a number');
}