It notifies you when someone comments on a meme, you also commented on.

This is actually an old option. They disabled it a while ago, but never cared to ask why.

I saw it for the first time last night. I tried it, but already disabled it lol

I disabled it lol

This notification type has actually existed since the beginning but it was disabled a long time ago for this exact reason, once the community started to become more active. A few people have started to take advantage of this setting now that it can be enabled manually though.

Seen it a lot. Though I tend to comment on what I find interesting and of course that is based upon whether I can think of a good comment. I don't like to spam a generics "LOL" or what ever just for the sake of commenting. But I guess that's neither here nor there.