What's an elf? For a lot of people, it seems to come down to pointy ears. (See any discussion about the accuracy of Talislanta's "No Elves" tagline line--which really seems to upset a lot of people--or discussion of Vulcans as "Space Elves.") Tvtropes, of course, has some ideas, but I feel like their definition only skirts the narrative use of elves in fantasy, mixing both surface characteristics and other qualities. My list overlaps in some places but has some differences. Not all elves or elf-like beings have all of these traits or possess the ones they do have to the same degree, but they tend to have the majority of them to a greater than humans (or whatever the baseline group of the setting is) in a work.
The qualities are:
- Otherworldliness. Magical, mythic, or nonmaterialness. This is probably the essential elven trait.
- Scale. Supra- or metahumanness.
- Alien. Nonhumanness in outlook/mentality.
- Morality. Association with greater moral clarity/absolutism.
Other qualities seem very common, but maybe not essential: "Clandestine/Hidden" and "Dwindling," are two the come to mind.
Tolkien's elves are perhaps only modest scorers except in Scale. Elquest elves are worse performs, but still outdo humans in several eras. The elves of Anderson's The Broken Sword, hit 3 out of 4 significantly. The Minbari of Babylon 5, ostensibly non-elves, manage to tic all the boxes.