What is the difference between 'reference height' and 'surface'?

[xlong@ncsu_edu]

In the output file,

There is a TREFHT Reference height temperature"
and a TS, Surface temperature (radiative)

What is the difference between them?

Is the reference height the same as surface?
Thank you

 

[fischer]

TREFHT is the air temperature at 2 meters.
TS is the temperature of the surface.