Isotropic and anisotropic are two terms that are used when describing certain properties of materials. The main difference between the two terms is that the properties of isotropic materials do not change when placed in different directions, whereas the properties of anisotropic materials tend to change when placed along with different directions.
In other words, isotropic materials are direction independent, whereas anisotropic materials are not i.e., they are direction-dependent. When you change the crystallographic orientation of isotropic materials, it won't affect their properties such as physical, electrical, mechanical, and thermal properties.
However, if you do the same to anisotropic materials, their properties tend to change. As a result of this, anisotropic materials tend to have two or more refractive indices, whereas isotropic materials have just one refractive index. The implication of the multiple refractive indices of anisotropic materials is that it causes them to show certain properties such as dichroism, birefringence, and optical activity.