The term "defamation" covers any statement that hurts someone's reputation. If the statement is made in writing and published, the defamation is called "libel." If the hurtful statement is spoken, the statement is "slander." Defamation is considered to be a civil wrong, or a tort. A person that has suffered a defamatory statement may sue the person that made the statement under defamation law.
Defamation law changes as you cross state borders, but there are some accepted standards that make laws similar no matter where you are. Generally in order to win your lawsuit, you must show that someone published a false statement that caused you injury, and that the statement did not fall into a privileged category.
Higher Burdens for Public Officials and Figures
People in the public eye get less protection from defamatory statements and face a higher burden when attempting to win a defamation lawsuit. When an official is criticized in a false and injurious way for something that relates to their behavior in office, the official must prove all of the above elements associated with normal defamation, and must also show that the statement was made with "actual malice," meaning that public officials could only win a defamation suit when the statement that was made wasn't an honest mistake and was in fact published with the actual intent to harm the public figure. Other people in the public eye must also prove that the defamatory statements were made with actual malice.