Some author said it. That the first death is the physical one, the death of the body. And the second one is when people stop sayin' your name, when they actually forget about you.

[ ...... ]

We don't remember his name, or what he looked like, or what he did...are we gonna forget that we even came down here to get him, at one point? We can't draw him, write down anything about him, record anything.

It's the 'second death.'