delete_post
delete_post is an action that is triggered when a post is deleted. It passes the ID of the deleted post. Note that at this time, the post has not yet been deleted.
This hook is an action which means that it primarily acts as an event trigger, instead of a content filter. This is a semantic difference, but it will help you to remember what this hook does if you use it like this: add_action('delete_post', 'your_function');