Regression \Re*gres"sion\ (r?*gr?sh"?n), n. [L. regressio: cf. F. r['e]gression.]

The act of passing back or returning; retrogression; retrogradation. --Sir T. Browne.

Edge of regression (of a surface) (Geom.), the line along which a surface turns back upon itself; -- called also a cuspidal edge.

Regression point (Geom.), a cusp.

Source: Webster's Revised Unabridged Dictionary (1913)