Nirvana is defined almost entirely by what it is not, and the tradition is deliberate about that. It is not annihilation — the Buddha explicitly rejected that reading — and not a paradise, and not the self surviving in a purified form, and the texts refuse the question of what happens to an awakened being after death as improperly framed, like asking which direction a fire went when it went out. The image is exact: a flame does not travel anywhere when it stops; it simply stops being sustained. What is extinguished is the burning of greed, hatred and delusion. Nirvana with residue is the state of a living awakened person, who still has a body and gets hungry; nirvana without residue is what happens when that body ends.