Wetland delineation is simply the act of establishing the boundary between wetlands and uplands (or non-wetlands). There are two delineation procedures developed at the federal level and several states have their own wetland delineation procedures.
The most important document is the 1987 Corps of Engineers Wetlands Delineation Manual which can be used for wetland delineations associated with both the Clean Water Act and the Food Security Act. The regulatory program developed under the Food Security Act is administered by the USDA, Natural Resources Conservation Service (NRCS) and you will need to refer to their current guidance on this matter.
For reference purposes we have included a copy of the 1989 Federal Manual which Congress withdrew in 1991.