Anisotropic means having different properties in different directions. Opposite: isotropic (having uniform properties in all directions).
A material is anisotropic when it has different properties in different directions, for example stiffness or conductivity. The plasma effect can be set to be isotropic or anisotropic. Particularly when etching microstructures, anisotropic effects are desired, i.e. a strong preferred direction of the etching speed.
The anisotropic effect is present primarily in physical etching processes (ion etching, RIE).