In the German language, perhaps the term "Weltschmertz" (loosely translates as "the pain of the world") comes as close as anything to summarizing what lies behind existential depression.

I wasn't so familiar with "Weltschmerz" in German. Intuitively, I wouldn't necessarily associate it with existential depression. Although I haven't had any experience of that either.

In most cases, these are transient situations that can be successfully addressed with therapy, pharmaceuticals, or both.

I wouldn't describe the three examples you mentioned as depression. Isn't the feeling of losing a close relative more like grief? It's okay to be sad, it's okay to be sad for a long time. For me, it's not an illness, but a feeling. Isn't depression rather the absence of feelings?

That's why I come back to your first sentence and have to agree with you:

We hear the term "depression" quite often, in our modern stressed-out world.

Nevertheless, it is good that depression is not hidden. In the past, real depression was far too often not recognised.