[The tone makes it clear that it's not an insult, and Sabriel's been called far worse, anyway.]

Those spirits that were once alive, but are no longer, and who have not yet passed beyond the Ninth Gate. Mostly, the term refers to those who seek to return to the world of Life, and try to resist the current.

[And lose both their humanity and human shape in the process. Kerrigor might have been an exception once, if he had been able to fool Touchstone and the royal family all those centuries ago, but he had been freshly dead then. Sabriel had seen his most recent body, which looked like something made by someone who'd never seen a human, but heard them described.]