A debunker is a person or organization that exposes or discredits claims believed to be false, exaggerated, or pretentious. The term is often associated with skeptical investigation of controversial topics such as UFOs, claimed paranormal phenomena, cryptids, conspiracy theories, alternative medicine, religion, or exploratory or fringe areas of scientific or pseudoscientific research.

According to the Merriam-Webster online dictionary, to "debunk" is defined as: "to expose the sham or falseness of." The New Oxford American Dictionary defines "debunk" as "expose the falseness or hollowness of (a myth, idea, or belief)".

If debunkers are not careful, their communications may backfire – increasing an audience's long-term belief in myths. Backfire effects can occur if a message spends too much time on the negative case, if it is too complex, or if the message is threatening.