The term "Fermi level" is the term used to describe the top of the collection of electron energy levels at absolute zero temperature. At absolute zero the Electrons pack into the lowest available energy states and build up a "Fermi sea" of electron energy states. Fermi level is the surface of that sea at absolute zero where no electrons will have enough energy to rise above the surface.
I am pasting here one flow chart just for your basic understanding.
Hope it gives you the basics.