Generalize the interactions in an Ising spin model, so interaction strength becomes a variable, dependent on the lattice site:
Consider the model where the strength is constant in magnitude
, but varying in sign, i.e.,
Suppose we choose the sign at random for every i,j link. This will introduce frustration, since not all links around certain plaquettes can be satisfied.
Randomness and frustration are hallmarks of real systems called spin glasses.