The concept that succesive iterations of a system bring about growth of the form X(n+1)=X(n)^Y.

Moore's Law is an example of exponential growth, with X being processing speed, n being an 18 month period, and Y being 2.

Exponential Growth is in essence any geometric progression with a common ratio greater than 1!

If the common ratio was less than 1 then it would become exponential decay instead!

The exponential function is a special case, where the common ratio is equal to e.

Comment on mrichich's writeup:
As I recall, Moore's law states that the number of cirquits that can be fitted on a given area of silicon will double in eighteen months. That means the function would look something like

X(n)=X(n-1)*2

or, non-iteratively

X(n)=X(0)*2^n

A rate of growth of an organism, a part of an organism, or a population of organisms which, when graphed, produces an exponential or [logarithmic curve. Such a rate occurs, for example, during the exponential growth phase, when a population of bacterial (or other) cells divide at a constant rate so that the total number of cells doubles with each division.

---

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.