Discovery, while I am not a lawyer, is now one of my favorite words. In lawsuits, it means that if Trump accuses you of terrible things, defaming him or whatever, you get to get his own records and recording of what he said and did, in order to discover and show the truth to a jury.
And yeah, the truth is in short supply whenever Trump attacks someone for opposing him. One thing Trump is not, he is not in any way someone who supports the First Amendment's protections for free speech.
It is why our new Greek Ambassador isn't going to sue anyone anytime soon...there are actual recordings of her bragging about her "pay to play' actions.