réseau

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

• noun A net or mesh foundation for lace.
• noun Astronomy A reference grid of fine lines forming uniform squares on a photographic plate or print, used to aid in measuring the relative positions and sizes of objects in the photograph.
• noun A mosaic screen of fine lines of three colors, used in color photography.

from The Century Dictionary.

• noun In lace-making, the ground when composed of regular uniform meshes, whether of one shape only or of two or more shapes alternating.
• noun A network of small squares formed by two sets of fine, parallel, equidistant lines, some millimeters apart, crossing each other at right angles, accurately ruled upon a glass plate.
• noun A diffraction grating. See grating, 2 .
• noun a sort of network of regions alternately distinct and blurred, covering the sun's surface, according to the earlier photographs of Janssen made with wet plates. Later results, however, seem to indicate that the phenomenon was not solar but purely photographic.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Astron.) A system of lines forming small squares of standard size, which is photographed, by a separate exposure, on the same plate with star images to facilitate measurements, detect changes of the film, etc.
• noun In lace, a ground or foundation of regular meshes, like network.

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

• noun a network of fine lines used by astronomers as a reference for measurements on star photographs
• noun a net or mesh foundation for lace