δ-box

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.