What makes denial denial and not just a refusal to admit to or accept a truth or fact rests in the degree of an individual's awareness of the existence of the truth or fact. In denial, an individual does not see or is mostly unconscious of existence of the truth or fact.
Rationalization encourages irrational or unacceptable behavior, motives, or feelings and often involves ad hoc hypothesizing. This process ranges from fully conscious (e.g. to present an external defense against ridicule from others) to mostly unconscious (e.g. to create a block against internal feelings of guilt or shame).
Regression (German: Regression), according to psychoanalyst Sigmund Freud, is a defense mechanism leading to the temporary or long-term reversion of the ego to an earlier stage of development rather than handling unacceptable impulses in a more adaptive way.
Repression and suppression are very similar defense mechanisms, which people use in order for them to cope with a stimulus that can harm them. What is suppression? Suppression is a useful psychological mechanism; here we force the unwanted information out of our awareness.
In psychology, sublimation is a mature type of defense mechanism, in which socially unacceptable impulses or idealizations are unconsciously transformed into socially acceptable actions or behavior, possibly resulting in a long-term conversion of the initial impulse.