Isotropic means "independent of 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.
Mathematics: Isotropy is also a concept in mathematics. Some manifolds are isotropic, meaning that the geometry on the manifold is the same regardless of direction. A similar concept is homogeneousness. A manifold can be homogeneous but not isotropic.
Radio broadcasting: In radio, an isotropic antenna is an imaginary "device", used as a reference; an antenna that broadcasts equally power (calculated by the poynting vector) in all directions. Decibels relative to an isotropic antenna are expressed as dBi or dB(i).
Physiology: In skeletal muscle cells (a.k.a. muscle fibers), the term 'isotropic' refers to the light bands (I bands ) that contribute to the striated pattern of the cells.
See also: anisotropic