Rudy Sued for 1.3 Billion for Defamation. What IS Defamation?

Former Bexar County DA Nico LaHood on the case being brought by Dominion against Rudy Giuliani. What is defamation? Slander? Libel? And, was this a smart move by Dominion knowing Rudy now can get access to the actual machines used on 11/3 -- unaltered.