Isotropy is uniformity in all orientations; it is derived from the Greek
isos (ἴσος, "equal") and
tropos (τρόπος, "way"). Precise definitions depend on the subject area. Exceptions, or inequalities, are frequently indicated by the prefix
an, hence
anisotropy.
Anisotropy is also used to describe situations where properties vary systematically, dependent on direction.
Isotropic radiation has the same intensity regardless of the direction of
measurement, and an isotropic field exerts the same action regardless of how the test
particle is oriented.