'Foul' in the Bible

Then I saw three foul spirits, resembling frogs, issue from the mouth of the Dragon, from the mouth of the Wild Beast, and from the mouth of the false Prophet.

and with a mighty voice he cried out, saying, "Great Babylon has fallen, has fallen, and has become a home for demons and a stronghold for every kind of foul spirit and for every kind of foul and hateful bird.