Someone who focuses on preparedness, generally for various worst-case scenarios like peak oil or armageddon. Sometimes used to avoid the more loaded term survivalist.
a person who believes a catastrophic disaster or emergency is likely to occur in the future and makes active preparations for it, typically by stockpiling food, ammunition, and other supplies.
A network of survivalists, patriots and Preparedness minded folks who wish to survive and prepare for disasters of all types; natural, man-made, and economic
Obviously, the word stems from the root word, prepare. It seems to me, a prepper could be basically anyone who likes or tries to be prepared for all contingencies, but seems to particularly imply preparedness for either small and large disaster scenarios.
(This word is NOT to be confused with the word, preppy, which has quite a different meaning.)
I was never really a preppy (even though I went to a prep school), but now I'm preparing to become a prepper, since these 2016 elections are putting the shit so close to the fan!
Not all preppers are the fanatics that are described or implied by some definitions. If you live in a place like California, especially if you live on a major fault line like I do, you really need to be a prepper; because when you run out of potable water, I'm not sharing mine with you! :p