In WordPress theme development, the code
if (! defined('ABSPATH')) {
exit; // Exit if accessed directly.
}Is typically used as a security measure to prevent direct access to the PHP files of the theme.
This code checks whether the constant ‘ABSPATH’ has been defined. ‘ABSPATH’ is a predefined content in WordPress wp-config.php file bottom. that specifies the absolute path to the WordPress installation directory.
If `ABSPATH` has not been defined, it means that the PHP file is being accessed directly rather than through WordPress and the code within the if statement will be executed.
By including this code at the beginning of a PHP file, the developer can ensure that the file is only accessed through WordPress and prevent any unauthorized access.
This can help to protect the security of the WordPress installation and prevent malicious attacks on the site.