A spin glass is a type of disordered magnetic material where the magnetic moments, or "spins," of atoms are frozen in a random arrangement. Unlike regular magnets, where spins align uniformly, in a spin glass, they can be oriented in various directions due to competing interactions. This results in a complex energy landscape, making it difficult for the system to reach a stable state. Spin glasses exhibit unique properties, such as slow relaxation and memory effects, which are studied in statistical mechanics and condensed matter physics. They are relevant in understanding complex systems, including neural networks and optimization problems, due to their intricate behavior and disorder.