Not my setting, but the one I'm playing in now, it's from SoS, the threads of which you can check out on /tg/.
The "Din," or Elves, are a broad genus of humanoid races who are distinguished by having a "focus" that can grant them immortality. They live forever so long as they fulfil the Focus, and if they stop fulfilling it, they begin to age until they fulfill it again.
They seem to share a root ancestor, but it isn't clear who it is.
The Ohanedin's focus is never breaking their word, and not eating the flesh of any animal that cannot speak. They are also burned by iron. They live in some mountainous forests, and generally only emerge to raid nearby settlements for metalwork and captives.
The Burdinadin's focus is avoiding exposure to nature. They live in gigantic iron fortresses, where they have developed technology centuries ahead of everyone else.
The Orredin's focus is each other. So long as they live in a certain concentration, they are immortal. But, they have weak constitutions that are susceptible to disease, so a high level of sanitation is necessary to avoid a plague that would wipe them all out. They mostly live in a flying magic city.
The Sugaardin's focus is being at sea with a certain number of their own kind. These groups develop a sort of psychic bond, which includes their ship, which becomes sentient so long as they retain this bond.
Some of the Din consider humans to be Din as well, but they believe that their focus is dying with valor. Dead humans sometimes return as ascendants, or Paladins, immortal beings in service to a powerful entity (some would say a god). Those who consider humans to be part of their little elf club call them the Hostoadin.
All of the name are Basque or something, there was a running joke in the threads that Paladin technically means "Shovel-Din" in that language, which might be a reference to the fact that humans can only become immortal by dying and being buried.