1. The process or an instance of regressing, as to a less perfect or less developed state.

2. Psychology Reversion to an earlier or less mature pattern of feeling or behavior.

3. Medicine Subsidence of the symptoms or process of a disease.

4. Statistics A technique for predicting the value of a dependent variable as a function of one or more independent variables in the presence of random error.

5. Astronomy Retrograde motion of a celestial body.

6. Geology A relative fall in sea level resulting in deposition of terrestrial strata over marine strata.