The races who worshipped the God of Light in the World of Firuman had a term for all dark creatures who hailed from the abyss. They were collectively termed as demons.
Just as how there were many races in the World of Firuman, there were also different kinds of demons in the abyss varying in strength. Not all demons were as strong as Tarviss or the Lord of the Deep, Nozama.
However, there was still no denying that demons possessed combat capabilities way above that of the races in Firuman. This applied to every single demon, more specifically, it was termed the "Abyssal Attribute".
In most cases, it would be difficult for a Firuman race to defeat a demon if they were of the same level of strength.