Psychologists use the term 'personality' to refer to the features of our psyche which make each and every one of us psychologically unique. One of the first personality theorists was Sigmund Freud. Freud is the best-known figure ever to emerge from psychology, and his theory of personality development has had a major impact on society and the way we think. Among other things, Freud is responsible for our concern about the meaning of dreams, and the embarrassment we experience concerning what slips of the tongue reveal about our unconscious thoughts. He drew attention to the irrational side of human behaviour, which had been largely neglected by other psychologists, particularly developmental psychologists. He is responsible for the common use of the terms 'ego' and 'defence mechanisms'.