A grueling process being forced upon you by circumstances / management that requires an unhealthy amount of hours, stress, etc to achieve to a (potentially unreasonable) objective by a certain time.

Likely outcome to meet the criteria is burn-out / resignation / death of personnel, especially if repeated.

In the original context, it is of course: https://en.wikipedia.org/wiki/Bataan_Death_March

I don't doubt that Bataan is the original, original context, but as far as software engineering goes, the term comes from this book:

https://www.amazon.com/Death-March-2nd-Edward-Yourdon/dp/013...

To me, the concept also includes that it's all for naught, since the project fails anyway.

That's correct:

https://en.m.wikipedia.org/wiki/Death_march_(project_managem...

The source:

https://www.amazon.com/dp/013143635X

You continue even though you're doomed to fail.

Yes, this. A death march, to me, is a project that is doomed to fail, but you have to keep working on it anyway.

No, a death march refers to the pace of the march, i.e. you're marching so hard (without rest) that you start losing troops to fatigue or worse.

I've heard Death March more meant as a crazy period before a deadline.