1 a backward movement, esp. a return to a former state.
2 a relapse or reversion.
3 Psychol. a return to an earlier stage of development, esp. through hypnosis or mental illness.
4 Statistics a measure of the relation between the mean value of one variable (e.g. output) and corresponding values of other variables (e.g. time and cost).
Etymology: L regressio (as REGRESS)
Useful english dictionary. 2012.