There is no single idea that is freudian theory, rather it is a collection of ideas related to Sigmund Freud's work on psychoanalysis:

Many of his (Sigmund Freud's) ideas have become universally familiar in a vulgarised form, e.g. the Oedipus complex, the death wish, the family romance, penis envy, phallic symbolism...

- from The Oxford Companion to English Literature.

Many people in freudian-denial object to, and are even disgusted by, Freud's ideas which only seems to give them further credence.