I'm sure nontechnical people use the term "exponential" loosely, but this being HN, I think clarification is in order. Consider the function f(x) = x ^ 2 (

I'm sure nontechnical people use the term "exponential" loosely, but this being HN, I think clarification is in order. Consider the function f(x) = x ^ 2 (where the caret stands for exponentiation, of course). This is called a quadratic function. Here are some example values: 0 1 2 3 4 5 6 7 8 9 0 1 4 9 16 25 36 49 64 81 This is the kind of relationship you have described: when x is doubled, f(x) is quadrupled. Now consider this function: f(x) = 2 ^ x This is an example of a function that is properly called exponential. Here are some example values: 0 1 2 3 4 5 6 7 8 9 1 2 4 8 16 32 64 128 256 512 Here, every time x increases by 1, the value is doubled. See how much faster it grows? In very practical terms, the difference between a "power law", as functions of the form x ^ k are called, and an exponential, of the form k ^ x, is massive. I grant that the terminology may be a little confusing, but this is not a pedantic distinction!