Generally, regression is a move backwards; It is the opposite of progress. Specifically:

• A term for the exploring, for example with the assistance of a therapist, of (possibly unpleasant) past memories (some believe even past life, see past life regression) as part of the treatment for mental illnesses or self improvement. See psychotherapy, hypnotherapy.
• A re-introduction of a defect into a later revision of a product. See engineering, regression testing.
• The phenomenon by which the sea retreats, or regresses, as a consequence of lowering sea level. See Transgression (geology).

• In statistics:
  • The phenomenon, that, when two related variables are measured, the expected value of the second is closer to the mean than the measured value of the first. See regression toward the mean.
  • A method where the mean of one or
    
    
    
    more random variables is predicted conditioned on other (measured) random variables. See regression analysis.

• The fictional reverse of the normal flow of time. In many animated television series this is usually shown as the characters' being turned back into children.

• In reading, regression is going back to re-read something recently read. Speed reading courses often discourage this.

• In psychology, regression is believed to be a defense mechanism of the ego, where a person reacts to failure with an immature response.

• In philosophy and theology, infinite regression is a problem discussed in the cosmological argument.

• In music, it is the first scene/song in Dream Theater's concept album, Scenes from a Memory.

Regression Regresyon