what exactly is the difference between a shotgun with a rifled barrel, in lets say 20 gauge, and a bore gun in 20 bore??

Is this a bore gun or rifled shotgun? CSM rifled gun

I just moved to Iowa and guess what NO center fire rifle deer season, well that's not exactly true as a resident I can hunt with a center fire during the last firearms season of the year(2 wks) and only antlerless.

thanks
mike