Denial is a defense mechanism postulated by Sigmund Freud, in which a person is faced with a fact that is too uncomfortable to accept and rejects it instead, insisting that it is not true despite what may be overwhelming evidence.  The subject may use:
* simple denial - deny the reality of the unpleasant fact altogether
* minimisation - admit the fact but deny its seriousness (a combination of denial and rationalisation), or
* projection - admit both the fact and seriousness but deny responsibility.