Definitions for "Inverse-square law"
Any law describing a force or other phenomenon that decreases in strength as the square of the distance from some central reference point. The term inverse-square law is often used by itself to mean the law staling that the intensity of light emitted by a source such as a star diminishes as the square of the distance from the source.
Illuminance at a point varies directly with the intensity, I, of a point source and inversely as the square of the distance, d, to the source. E = I/D, where D = d*d.
The law that a field follows if its strength decreases with the square of the distance. Fields that follow the inverse square law rapidly decrease in strength as the distance increases, but never quite reach zero.