A Freudian slip is a verbal or memory mistake that is believed to be linked to the unconscious mind. Common examples include an individual calling his or her spouse by an ex's name, saying the wrong word or even misinterpreting a written or spoken word.
Discovered by Sigmund Freud, he described a variety of different types and examples of Freudian slips in his 1901 book The Psychopathology of Everyday Life. According to Freud, these errors reveal an unconscious thought, belief or wish.
"Two factors seem to play a part in bringing to consciousness the substitutive names: first, the effort of attention, and second, and inner determinant which adheres to the psychic material," Freud suggested in his book. "Besides the simple forgetting of proper names there is another forgetting which is motivated by repression," Freud explained (1901). According to Freud, unacceptable thoughts or beliefs are withheld from conscious awareness, and these slip help reveal what is hidden in the unconscious.
The term is popularly used today in a humorous way when a person makes a mistake in speech. In these situations, observers often suggest (in a comic way) that the mistake reveals some type of hidden emotion on the part of the speaker.