I will first give you the definition from Google then I will give you the definition from the word of God and what the Lord tells us how to handle this sort of thing.
Google: To attack the character or reputation of a person who is not present or to speak unfavorably or slanderously of a person who is not present.
The Word Of God: This know also, that in the last days perilous times shall come For men shall be lovers of their own selves, covetous, boasters, proud ,blasphemers, disobedient to parents, unthankful, unholy, without natural affection, trucebreakers, false accusers, incontinent, fierce, despisers of those that are good. Traitors, heady, high-minded, lovers of pleasures more then lovers of God ;Having a form of godliness, but denying the power thereof: From Such Turn Away.
Note: The word of God tells us to turn away from these people . when they do this it slanders some ones corrector . It can be a form of witchcraft because you manipulated what someone else thought of that other person we have all been guilty of this one time or another in our lives we need to repent and not do it anymore. and turn away from people doing this also.
Note: In the bible it tells us these people are our enemy and what to do about it as well .
Provers 25:21-23 If thine enemy be hungry, give him bread to eat; and if he be thirsty, give him water to drink: For thou shalt heap coals of fire upon his head, and the Lord shall reward thee, The north wind driveth away rain: so doeth an angry countenance a Back Biting Tongue.
May God Bless You