FEMA Definition:

“The computed elevation to which floodwater is anticipated to rise during the base flood. Base Flood Elevations (BFEs) are shown on Flood Insurance Rate Maps (FIRMs) and on the flood profiles.

The BFE is the regulatory requirement for the elevation or floodproofing of structures. The relationship between the BFE and a structure's elevation determines the flood insurance premium.”

In other words, the bottom of the subfloor of your home must be above the stated BFE in order to be considered “out” of the floodplain. You may need a “Certificate of Elevation” from a licensed land surveyor in order to prove that your home is out of the floodplain.

Learn more at: http://www.fema.gov/plan/prevent/floodplain/nfipkeywords/base_flood_elevation.shtm