(law) Abbreviation of defendant.

(of a topological space) In which every geodesic triangle satisfies that every point on the triangle is within a distance of δ (some constant) of each side of the triangle.

(mathematical analysis) A k-cell which is a Cartesian product of half-closed intervals which are closed at their infima and open at their suprema, and such that the infimum of each interval is the coordinate of a given point (called "the corner" of the δ-box), and the length (i.e., measure) of each interval is equal to (the given value) δ.

plural of δ-box