Form birefringence refers to the birefringence caused by anisotropy in the form (shape) of an object, typically a crystal, fiber, or film. Synonyms for form birefringence include shape birefringence, dimensional birefringence, morphology birefringence, and anisotropic birefringence. Other related terms include strain birefringence, which occurs when a material undergoes mechanical stress, and intrinsic birefringence, which is caused by the inherent anisotropy of a material's optical properties. Understanding the different types of birefringence is important in fields such as polarization microscopy, optical materials science, and bioimaging.