damp course, damp check, dampproof course
In masonry, an impervious horizontal layer of material (as tile, dense limestone, metal, etc.) to prevent the capillary entrance of moisture from the ground or a lower course, but used also below copings, above roof level in chimneys, and elsewhere to stop downward seepage.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.