Parapraxis is the technical term for a Freudian slip: an unintentional slip that reveals repressed emotions or thought patterns. It is said to be more common when the subject is distracted, excited, or asked to recall things unexpectedly. Freud believed that this revealed language to be a common defense mechanism of the brain, and that shielding one's thoughtscan impede psychological progress.
Parapraxis is not limited to verbal misfires. For example, if while going about your business you find yourself in one room in your house when you had intended to end up in another you may be avoiding some unconscious conflict or undesirable situation in that room.
Parapraxis may also work in reverse: tip of the tongue, or TOT, phenomenon is also often attributed to parapraxis, as the brain chooses to repress undesirable thoughts from emerging, even in seemingly innocuous settings and conversations.
The word itself comes from Greek words para, meaning "beside", and praxis, meaning "action", and is often translated as "diverted action" or "underlying action." It was actually coined by the famous Welsh neurologist and Freud biographer Ernest Jones, as he often took to translating Freud's new German medical terminology into Latin and Greek-based words (with Freud's tacit approval) for English-speaking audiences.
The concept behind this term has been under considerable scrutiny since its introduction into modern psychology: Freud's own word, Fehlleistung, translates roughly as "faulty achievement", implying an unconscious success through a conscious failure. Parapraxis removes the "faulty" aspect of Freud's translation, substituting it for merely "underlying", which all but eliminates the psychological battle between conscious and unconscious self. Today the more practical "Freudian slip" reinstates the "fault" of the user, and benefits from the direct reference to Freud and his works. Still, parapraxis is commonly found in medical literature and enjoys technical use even today.