Now dont get excited, you still arent allowed to gossip. And I beleive we have covered most of the reasons as to why not. But the following are a few exemptions for certain people in certain circumstances.
1) A person who was treated unjustly. This person can go to a Judge or a Leader, complain to him and tell him of the person who has done injustice to him. Technically this is not backbiting because Allah (SWT) said in Surah Nisaa verse 148 what can be translated as "Allah does not like that the evil should be uttered in public, except by him to whom injustice has been done".
2) A person who is asking for fatwah (from a person with knowledge). A person may ask for an Islamic legal opinion, in this request he might talk about things that happened between him and somebody else - he may include some things which may not seem good, but Islam allows it as long as your intention is to know the ruling. This exemption is proved from the following tradition of the Prophet (pbuh)- reported by Bukhari:
3) Advising Muslims what is good for them. For example, when someone asks you about a person that you know whom they are going to marry, or about a business partnership, you are required to tell them the truth. The proof comes from the following story narrated by Bukhari:
4) Warning Muslims about enemies. If you know for sure that someone is an enemy of Islam, that they pretend to be Muslims from the outside, yet work, plan and think against Islam, then you are allowed to tell others for this person is a Hypocrite. There are many proofs to this exemption, the following one is reported from Bukhari:
5) When Identifying someone. It is considered backbiting when you refer to someone from his features such as short, fat, ugly, bald etc. But when identifying someone who really is deaf, blind, mute and handicapped as such - it is permissible.