Folding, adjustable and detachable stock question

[Sohum63]

Wasn't sure what section to post this in and didn't find anything with a search but what are they addressing in the AWB when talking about detachable stocks. The first thing that came to mind was the Henry AR-7 survival rifle (didn't see a rim fire eximption) but really a lot of rifles have a removable stock. Just wondering what kind of stock are they addressing here?

[S470FM]

the stock that makes the gun under 30" OAL.