Technically speaking, demons usually have higher magic potential, longer lifespan and, unless "defective", a racial power. Even the more human-like demons have something that sets them apart from humans.
Technically, demons where originally the dwellers of the Realm of Magic, but after the Laplace Wars the definition changed, and now demons are "those of races that sided with Laplace", which means basically those who have the Demon Continent as a homeland, which is why some former "demons", which are elves, dwarves and halflings (they used this naming convention, right?), as regarded as "humanish", with only the more staunch human supremacists discriminating against them, while some races that came from the Realm of Animals are regarded as "demons" since they live in the Demon Continent.
PS. has someone else's RSS feed mistakenly flagged a whole bunch of chapter as "unread"?