There is only one difference between a Demon and an Apparition, and that is that Apparitons carry the apearance of humans and sometimes have a demonic tranformation....only sometimes.
Demons do not have a human-looking form. The demon may be humanoid, meaning standing on two legs and having wings or something, but not carry the exact appearance of a human
Hopeful this answered your question otherwise, just PM me or another Admin and we'll straighten out any other misunderstandings.