Everything I had read was about semiconductors; since the band-gap is different for semiconductors and insulators, I'd to know if there is any difference between the concepts
The Fermi level is the energy level for which the probability of finding an electron, (a Fermion), is equal to 1/2. See Fermi -Dirac statistics. For both insulators and semiconductors the Fermi level lies in the band gap, (no available states for an electron to occupy).