This question came up yesterday so I thought it was a good idea to catch the details here
Orthometric Height is the distance (height difference) from the point to the geoid
Ellipsoidal Height is the distance (height difference) from the point to the ellipsoid
The difference between the two values is the Ellipsoid - Geoid separation (height difference) at the point.
I was then asked so what is the Geoid - Ellipsoid separation in Florida - this site is a useful resource if you want to determine the Ellipsoid - Geoid Separation at your location (defined in Lat / Long / Height).
UNAVCO - Geoid Height Calculator
Florida on the coast around Daytona Beach has a Geoid Separation of ~24’, inland that increases to -28’ for example. In Boulder CO we have a value of -19’ for example.
Hope that this helps