Satan is the step above Demons and Evil Deities. One that is meant to represent The Devil, the highest authority over Hell, one that is evil and corruption incarnate within his or her world, and the Inferno Counterpart of God. (It must be noted that the last point takes liberty with the monotheist religions, which depict the Devil as far inferior to God and states that the Devil is bound to be defeated.)

Interestingly enough, some stories portray the Devil in a sympathetic light, or even as an anti-villain as in South Park or Devilman. Some even portray him as just one of the sources of evil, if the God of the setting is also evil.

In short, this is meant to represent Satan himself or his closest in-universe counterparts - nothing less.

IMPORTANT NOTE: if an entity is said to be the opposite counterpart of a Supreme Being and holds equal power to said Supreme Being they are considered a true "Anti-God" and should be placed under Supreme Beings - they outrank Satanic entities (who are always significantly below the power of Supreme Beings)