The idea of a "Freudian slip" has become a punch line for many jokes with people accidentally saying something they think without meaning to say it. However, it is also a psychological term created by Sigmund Freud to support his model of psychoanalytic theory of personality.
In Freud's theory, he emphasizes the point of psychic determinism (meaning that all psychological events have some sort of cause). This includes even "slip of the tongue" experiences. Freud claims that all people have both unconscious and conscious minds: unconscious being the part of personality in which we're unaware, conscious being what we are aware of. So, a Freudian slip occurs when a person makes an unintentional error when speaking which ends up revealing their unconscious thoughts or feelings. This slip occurs due to particular circumstances that allow someone to reveal their true beliefs while they are having their own internal struggle between some unconscious wish along with a desire they have to keep it hidden.
However, the Freudian slip is also given much criticism for being inaccurate. There are instances in which speech is merely a mistake/accidental rather than having some underlying meaning. This is likely to happen in cases in which someone is merely inattentive, has insufficient knowledge, or they have a routine response pattern due to emotions or situations. Clearly, these cases have nothing to do with unconscious desires, rather they are simply mistakes. Yet, this doesn't mean that all wording accidents are a result of these causes. Psychologists agree that some of our slips are due to unconscious desires that are brought to the surface.
Thus, whether a verbal mix-up is a Freudian slip may depend upon the situation. Further questions to pursue include: is there any meaning behind our slips? And, if so, when are these slips a revelation of our unconscious and when are they simple cases of misspeaking? Regardless of the validity of the Freudian slip, Sigmund Freud's ideas were revolutionary, influencing others and generating novel discoveries in the field of psychology.