They ask you for a legal verdict. Say: "Allah directs (thus) about Al-Kalaalah (those who leave neither descendants nor ascendants as heirs). If it is a man that dies, leaving a sister, but no child, she shall have half the inheritance.
If (such a deceased was) a woman, who left no child, her brother takes her inheritance.
If there are two sisters, they shall have two-thirds of the inheritance; if there are brothers and sisters, the male will have twice the share of the female.
(Thus) does Allah makes clear to you (His Law) lest you go astray. And Allah is the All-Knower of everything."
[Qur’aan 4:176 – Translation by Muhsin Khan]
I fell ill, and the Prophet (sallallaahu alayhi wa sallam) and Abu Bakr came to me on foot to visit me. As I was unconscious, I could not speak to him.
He performed ablution and sprinkled water on me ; so I became conscious. I said: O Messenger of Allah, how should I do in my property, as I have sisters?
Thereafter the verse about inheritance was revealed: "They ask you for a legal verdict. Say: "Allah directs (thus) about Al-Kalaalah (those who leave neither descendants nor ascendants as heirs)."
[Sunan Abi Dawud – The Book of Shares of Inheritence – Chapter: Regarding Al-Kalaalah – Hadith No. 2886]
قال القسطلاني : الكلالة الميت الذي لا ولد له ولا والد ، وهو قول جمهور اللغويين ، وقال به علي وابن مسعود
According to the majority of scholars, al-kalaalah refers to the one who has no father(s) or son(s). Since grandfather(s), great grandfather(s), etc., and son(s) of son(s), etc., are regarded to be from the category of father and son respectively, the translation uses the word ascendants and descendants.
أو الذي لا والد له فقط ، وهو قول عمر . أو الذي لا ولد له فقط ، وهو قول بعضهم . أو من لا يرثه أب ولا أم . وعلى هذه الأقوال فالكلالة اسم للميت ، وقيل الكلالة اسم للورثة ما عدا الأبوين والولد . قاله قطرب واختاره أبو بكر رضي الله عنه . وسموا بذلك لأن الميت بذهاب طرفيه تكلله الورثة أي أحاطوا به من جميع جهاته
According to another group of scholars it refers to the person who has no ascendants only. A third opinion is that it refers to the one who has no descendants only. Another opinion is that it is a person who has no father or mother to inherit from him. Based on all the opinions mentioned so far, it becomes evident that Al-kalaalah is a noun for the dead person.
One opinion states that al-kalaalah is a noun for those who will inherit, excluding the parents [i.e. mother and father] and son. The reason they have been named al-kalaalah [based on this opinion] is because when both sides of the dead person have gone away [i.e. ascendants and descendants] then it is the inheritors who takallalla [encompass] him, meaning that they encompass him from all sides [i.e. since his wealth will be distributed among them].
[معنى تكلل في معجم المعاني الجامع]