So I went immediately to the Urban Dictionary and found this:

"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."

Now I know ETS states up front that it is not a survivalist forum (good!). There are alternative definitions of "prepper" in the UD, one of which emphasizes the negative aspects of the activity.

Reading on some threads, one does get the impression that many preppers will be really disappointed if TEOTW does come fairly soon - they have invested heavily.