what exactly is "Gheebat"?

Gheebat is basically undermining someone’s reputation etc. in his absence where he is not able to defend himself. Thats why backbiting is equated to eating flesh of a dead brother.

Here are the quranic verses

I think it is better to avoid such discussions. But if the matter is serious and someone asks your opinion in a matter like initiating a relationship then I think it is good to provide ‘awareness’ to the concerned party but without any exaggeration. I think in that case, it would not be ‘gheebat’ because your motive will be to save someone from committing a blunder. but I would like to hear from others if they have differing opinion in this case.