FEMA defines a FIRM as:
The official map of a community on which FEMA has delineated both the special hazard areas and the risk premium zones applicable to the community.
These FIRM's are important to a home owner because it shows if your home is in a flood zone and your insurance rates are based off of that information. Having a current Elevation Certificate can be used instead of the FIRM. Since 2012 many cities have new flood maps and this could greatly effect your flood insurance cost.