crystal lattice

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A geometric arrangement of the points in space at which the atoms, molecules, or ions of a crystal occur.

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

• noun crystallography A regular three-dimensional geometric arrangement of atoms, molecules or ions in a crystal

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a 3-dimensional geometric arrangement of the atoms or molecules or ions composing a crystal