Defamation is the all encompassing term referring to any statement that injure a person's reputation. There are two types of defamatory statements: libel and slander. Libel is defamation that is published or written. Slander is spoken defamation.
Defamation is considered a "tort" or civil wrong, meaning that it is not a crime and a person cannot be imprisoned for defamation, but they can be sued under the defamation law.
There is a fine line between what is considered defamation and what is protected under free speech.
If someone has hurt your reputation you can file a lawsuit against that person for defamation. In order to be successful in your case there are a few key facts you generally must present :
You must show that someone made a statement about you. This statement can be spoken, written, pictured, or gestured. Unless the person was recorded saying the statement, slander is difficult to prove, and usually less harmful because spoken word is fleeting, whereas libel, or a written statement is more easily recorded, and thus usually considered more harmful.
The statement must have been published. "Published" doesn't mean published in the traditional sense. It doesn't necessarily mean the statement has to be in a book or magazine, although it can be. It only means that the statement must have been seen or heard by a third party person. Some examples include: being heard on a radio, overheard in a loud conversation, seen on TV, seen on a flyer, or seen on social media.
You must show proof that the statement caused you injury or harm. You must be able to prove that the defamation caused your reputation harm with concrete evidence. Some examples of a damaged reputation could be lost job or shunned by friends. If a person already has a poor reputation they will have a very difficult time proving their case.
You must show that the statement was false otherwise it cannot be considered damaging. If a statement is proved true then it is not defamation. In order to win a defamation case, the plaintiff must prove that the statement was defamatory. A person cannot prove a statement of opinion false because it's subjective.
And the statement must be "unprivileged." The government has created laws that make certain statements privileged. For example, witness testimony in court is considered privilege. What they say under oath cannot be considered defamatory. This was put in place by lawmakers so that witnesses wouldn't feel constrained and worried that what they say could get them sued for defamation.
Public figures have a harder time proving defamation and usually have a higher burden and must prove that there was malice in the defamatory statements made against them. The public has a right to have opinions and criticism for those in the public eye, so officials and celebrities have the least protection.