ORIGINAL: Gruntr Huntr
From what I've read, game departments define 'feral hog' as being any hog, including domestic, which has been free to roam, unclaimed, for a certain number of days. So, seems like 'feral' is more of a legal definition than an actual subspecies? But, I know what you're talking about. To me, feral implies a species that has gone wild from domestic stock, over generations instead of days.
Here's a Link to a good "Definition Of Feral Hogs",
FERAL HOGS- STATUS AND DISTRIBUTION IN MISSOURI
And other States have their own Definitions andLaws about Feral Hogs
GENERAL REGULATIONS FOR hogs