Isotropy means uniformity in all directions. This is an assumption made about space, i.e., the universe which is one of the assumptions of the cosmological principle, in turn an assumption of the Big Bang theory. The absence of isotropy is anisotropy. Both terms are used regarding the cosmic microwave background to describe the fact that it comes at us from all directions: it is basically isotropic but has a small anisotropy that is of much research interest.
Isotopic radiation is radiation from a body that is emitted from it in all directions, i.e., like electromagnetic radiation (EMR) from a star. When an especially bright source is discovered, such as with a redshift showing great distance but observable, an immediate question is whether this is isotropic radiation or is anisotropic, e.g., beamed in our direction. If it is indeed isotropic, then its luminosity (its power; in this case, its isotropic radiant energy output) must be extreme and its high-luminosity mechanism is of research interest.