Some plugin is using “load-post-new.php” as action hook, what does it mean?

I’m trying to learn to develop for WordPress, and I came across something that I couldn’t understand. Hope someone can help.

A plugin I’m reviewing is using

add_action ('load-post-new.php','EasyPayPal_PostPayment');

I understand that add_action() takes an action hook as first parameter, and the function name as second parameter, so what is this load-post-new.php action hook? Does anyone know?

Thanks,