"O
you who believe! Avoid much suspicion, in deeds some suspicions are sins. And
spy not neither backbite one another. Would one of you like to EAT THE FLESH OF HIS DEAD
BROTHER? You would hate
it (so hate backbiting). And fear Allah, verily, Allah is The One Who accepts
repentance, Most Merciful" (Qur'an 49: 12) 
This
verse resembles a person who backbites to one who eats the flesh of his dead
brother.
How
does Islam define Backbiting?
Talking
about your brother in a manner which he does not like.
What
if my backbiting gossip is based on facts ?
If
the backbiting is based on facts then it is defined as backbiting. If you are
making the things up, then it is slander.
"Abu
Huraira reported Allah's Messenger (may peace be upon him) as saying: Do you know what is
backbiting? They (the
Companions) said: Allah and His Messenger know best. Thereupon he (the Holy
Prophet) said: Backbiting
implies your talking about your brother in a manner which he does not
like. It was said to him:
What is your opinion about this that if I actually find (that failing) in my
brother which I made a mention of? He said: If (that failing) is actually
found (in him) what you assert, you in fact have backbitten him, and if that is
not in him it is a slander. "[Sahih Muslim Book 32,
#6265]
