Anisotropy designates different character in different directions. It is the opposite of Isotropy what designates identical character in all directions.
A material has anisotropic characteristics, if those are different in different directions, for example its stiffness or its electric conductivity. Materials with anisotropic characteristics for example are wood or Advanced Composites, which both have much higher strength in direction of their fibre orientation.
Plasma treating can have isotropic or anisotropic effects. In particular for etching microstructures anisotropic effects are desired, i.e. significantly different etching effects in different directions.
Anisortropic etching is provided by physical etching methods like Ion Etching, Reactive Ion Etching (RIE), Micro Sandblasting.