On FEMA map in Zone AE, what does "2.5' depth criterion applies" mean?

[AskTooMuch]

I tried googling but not going anywhere.
Does it mean minimum of structure floor must be 2.5' above BFE of Zone AE?
I'm just looking at some properties not designing anything.

 

[cvg]

first (habitable) floor must be above the 100-year floodplain elevation. the floodplain manager or the building department may have other requirements.