This is a yes/no field that indicates whether or not a map unit component is classified as a "hydric soil".
A hydric soil is a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part. Hydric soils along with hydrophytic vegetation and wetland hydrology are used to define wetlands.
More information about hydric soils can be found at http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/use/hydric/
Source: U.S. Department of Agriculture, Natural Resources Conservation Service. National soil survey handbook, title 430-VI. Available online. Accessed 9/18/2012.