What was the actual End?

[Luinëcolloien]

In a lot of Tolkien's writings, and in a lot of writings about Tokien's writings, there is reference to 'The End.' By this I mean the real End. For example, someone said that 'even after the Ring was destroyed, there was still a shapeless shadow of evil lurking until The End' and somewhere in the Silmarillion it says about the awakening of Elves that these creatures would be immortal, and not die, unless being slain or of grief, and would live until The End. (that's not the exact quote, sorry). I was just wondering if anyone actually knows what The End was. What happened, are there any writings of it? Opinions appreaciated, thanks for reading!