An act of communication (whether written or oral) that tends to damage another's reputation to the extent of lowering their regard in the community or deterring others from associating with them (Restatement (Second) of Torts, Section 559). Slander (spoken false statements) and libel (written false statements, including statements published on the internet) are both forms of defamation. State law governs this cause of action, and the requirements for making a defamation claim generally vary by state.

Though the standard varies, most states generally follow the Restatement (Second) of Torts, Section 558, which outlines the elements of a defamation claim as: