what is meaning of backbite and why peoples backbite ?

Answer 1

To "backbite" is to say mean things behind someone's back - meaning when they're not around.

People backbite because they are petty or maybe because they want to feel superior - or just because they are plain immature.

Answer 2

Backbite is a term used to indicate betrayal.
To backbite is to betray, a backbiter is a traitor.
As for why people do it...
Greed, Lust, Envy, Anger, Pride...
Usually it makes the betrayed seem less than thier efforts would merit, and the betrayer seem more than thier efforts warrant.

Hope this is what you were looking for