Here is the definition of defamation according to Cornell: "Overview
Defamation is a statement that injures a third party's reputation. The tort of defamation includes both libel (written statements) and slander (spoken statements).
Elements
To prove prima facie defamation, a plaintiff must show four things: 1) a false statement purporting to be fact; 2) publication or communication of that statement to a third person; 3) fault amounting to at least negligence; and 4) damages, or some harm caused to the person or entity who is the subject of the statement."