A spin glass is a type of disordered magnetic system characterized by competing interactions among its magnetic moments (or "spins"). In physics, the term usually refers to a specific class of materials or models where the spins can be in a state that reflects a glassy (disordered) configuration, rather than aligning neatly as in ferromagnetic or antiferromagnetic materials.
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A spin glass has frozen, irregular local spin magnetization without the periodic magnetic order of a simple ferromagnet or antiferromagnet. Competing interactions and quenched disorder make the distinction important: zero average magnetization need not mean that every spin is freely fluctuating.[ref]
Solvable Model of a Spin-Glass by David Sherrington and Scott Kirkpatrick. pp. 1792–1794, introduction and interpretation of the frozen-moment order parameter
The frustrated Ising triangle gives a small example of incompatible local preferences. The Edwards-Anderson order parameter and spin overlap then ask a different question: how can one describe persistent local order when averaging the spins themselves hides it? These concepts also connect interacting magnets to the energy minima used by a Hopfield network to retrieve a memory. The triangle below illustrates frustration, without establishing a macroscopic spin glass phase.