Hi David and welcome. NFA = National Firearms Act and usually means the firearm has to be NFA registered and a $200 Tax Stamp paid. Cheers, stay safe and enjoy! atf.gov/rules-and-regulations/national-firearms-act

David, it typically means that the barrel is shorter than 18 inches. When it is, it is an NFA or Class 3 item. The terms NFA item and class III item are used to describe the same thing. When you think of an NFA/Class III item, folks are typically talking about a short barreled rifle (SBR) such as an MP5 with a stock, a short barreled shotgun such as one of the ones here that you are seeing, and then a suppressor/silencer. All these items are part of the NFA (National Firearms Act). To buy/posses one of these NFA items, you need to pay the ATF $200 for a "tax stamp" and then wait for the paperwork to get approved before you can pick it up from your FFL.