WordPress at a glance
action is not described

pre_comment_on_post action-hook . WP 2.8.0

Fires before a comment is posted.

Usage

add_action( 'pre_comment_on_post', 'action_function_name_2346' );
function action_function_name_2346( $comment_post_ID ){
	// action...
}
$comment_post_ID(int)
Post ID.

Where the hook is called

wp_handle_comment_submission()
wp-includes/comment.php 3081
do_action( 'pre_comment_on_post', $comment_post_ID );

Where the hook is used (in WP core)

Does not used.