LBan-1

In a system of $N$ degrees of freedom we have a number of configuration which is exponential in $N$. For instance, for a spin system on a lattice of size $L$ in dimension $d$, $N=L^{d}$ and the number of configuration is $M=2^{N}=e^{N\log 2}$ configurations. In presence of disorder the energy associated to a given configuration is random:

Since the systems are random, the quantities that describe their properties (the free energy, the number of configurations of the system that satisfy a certain property, the magnetization etc) are also random variables, with a distribution.