I have heard of a community garden, a community kitchen, and even a community cat. You know, pretty much anything in a shared area that different people in the community look after. But I had no idea that this concept also applies to guns, apparently widely enough to be blithely referenced in a news headline.
So basically this is a gun left in some easily accessible area that different people can come and get to use as they see fit. And it is a widespread enough concept that various states have laws against the practice or buy-back programs targeting them. I think I would be happier, honestly, not knowing that irresponsibility with guns goes so much further than I imagined.