n. The act of passing back or returning; retrogression.n. In astronomy, motion from east toward west.n. In geometry, contrary flexure; also, the course of a curve at a cusp.n. In mathematics, a discrete series which has a last element but no first.n. In statistics, the tendency of one variable phenomenon that is correlated with another to revert to the general type and not to equal the amount of deviation of the particular phenomenon with which it is correlated.n. In breeding, the decline toward mediocrity of offspring from the mean of the two parents. Sometimes called filial regression.