Question: How would you describe the **Power Law** in simple words? The Wikipedia entry is too long and verbose. I would like to understand the concept of the power law and how and why it shows up everywhere.

For example, a recent Economist article **[Cry havoc! And let slip the maths of war](http://www.economist.com/node/18483411)**, shows that terrorist attacks follow an inverted power law curve.

Answer: 
The power law just is the equation $f(x)=ax^k$ (the Wikipedia article allows some deviation.) If $k \lt 0$ it says that big events get less likely than small events and how fast. It shows up many places in science, and finding the exponent is often a clue to the underlying laws. It also shows up in the real world. [This paper](http://www.hpl.hp.com/research/idl/papers/ranking/adamicglottometrics.pdf) discusses finding it in statistics on the internet. Of course, real world data doesn't fit a power law exactly, and how close is "close enough" may be in the eye of the beholder. It is also known as "Zipf's Law" if you want to search around for places it is found.
An easy to read article with data: <http://www.jmir.org/2015/6/e160/>