Power Law
The power law defines a relationship between two quantities where a relative change in one quantity $a$ gives rise to a proportional relative change in the other quantity $b$. The most common example for this relationship is the area of a square in regard to the length of a side. If the length is doubled then the area is multiplied by a factor of four. A similar example where if the length of a side of a cube is doubled then the volume the cube is multiplied by a factor of eight.