Definition: Anisotropic refers to a phenomenon where particles move at different speeds in three dimensions, making them appear as though they are spread out rather than concentrated together. This effect is found in materials like glass or ceramics, which have anisotropies that make their properties vary with their orientation. The word "anisotropic" comes from the Greek words "aniso," meaning "none," and "tropic," meaning "directional." The term was first used by German physicist Wilhelm Heisenberg in his work on quantum mechanics, which described how particles behave under certain conditions.