Devil means the supreme evil spirit according to the Christian or Jewish mythology. The devils reside in hell, which is their abode. The word “devil” also refers to a cruel or wicked person, who has nefarious designs or impish ideas in his mind all the time. People indulging in all sorts of wrong deeds are not treated respectfully, by the society. They are referred to as devils.
In the words of James A. Garfield, “A brave man is a man who dares to look the devil in the face and tells him that he is a devil.” At times, mischievous kids who indulge in naughty mischief are also called “devilish”. So, devilry can be either interpreted as a wicked or cruel activity or simply as, reckless mischief. Another term that is used is “devil's advocate”. It refers to any person who supports unpopular opinion, in order to start a debate.