The pathogenic process which is demonstrated by the resistances we call REPRESSION. It will now be necessary to make our conception of this process of repression more precise. It is the essential preliminary condition for the development of symptoms
Freud defines repression as the pathogenic process evidenced by resistance, constituting the essential precondition for symptom formation and distinguishable from mere repudiation or condemnation of an impulse.
, Introductory Lectures on Psycho-Analysis, 1917thesis