What is the physical meaning of the fermi level in semiconductors?

[Eng.]

I Know that the fermi level in an intrinsic semiconductor is found between the valency level and the conduction level in the energy gap , and I know that also when the semiconductor is doped the fermi level either move toward the conduction band or away from it.But actually I can not get the physical meaning of the fermi level, so I would be glad if someone helped and thank you>

 

[Enthalpy]

It's the energy at which the probability of occupation of a level changes from high to low.

Which needs a level, of course. There is none in the forbidden band.