It certainly is here in the northern latitudes. But I wouldn't be surprised if someone in Florida has never heard of it.

I'm dumb, and for a minute I thought the parent was putting a lot of emphasis on their sadness during the winter.

This specific acronym is IMO a bit too appropriate for the subject.

It's a well-known concept here in northern Europe, and I must have seen the acronym before, but I did not recognize it.

Based on what ?