Another special type of logarithm you'll see from time to time is the natural logarithm, usually written as ln(x) instead of log(x). We like to think the "n" comes after the "l" because it stands for log au naturel.
A natural log is the same as a regular log, except it has a base of e instead of 10. If you haven't met him before, e is an irrational number that represents the sum of 
and so on.
Weird, right? But it's really useful! You'll see the natural log all the time in higher-level math, but we'll show you a common use in a later chapter. For now, just remember this:
ln x = loge x
To confuse things, some people write ln x as loge x or even log x. We wouldn't do that; keep an eye out, though!