What will "the end of the world" be like?

We see lots of questions here about "the end of the world" but I'd like to ask exactly what you think this means. By "world" do you mean the human population of Earth, all life on Earth, the Earth itself, or the whole Universe? How do you envisage this "end": famine, disease, hellfire? Most important, what _physical process_ will this entail? What mechanism will bring about this "end"?