Khums" literally means "one-fifth. In Islamic legal terminology, it means "one-fifth of certain items which a person acquires as wealth by means of farming, trade, industry or by means of working in an office or government department and if his earning exceeds the annual expenses for maintaining himself and his family, he should pay Khums (i.e. 1/5) from the surplus, in accordance with the rules.
Khums is one of the Islamic obligations which the Quran has mentioned alongside Jihad. There are reasons and secrets behind the obligation of Khums some of which we will mention as under:
1. Khums has been made obligatory to meet the expenses of the Imam (a.s) as the leader of the government in order for him to run the Islamic government as well as the affairs of society. That is why, in some traditions, Khums has been referred to as wajh al-Imarah (cost of the Islamic emirate).
2. In order for God, the Exalted, to maintain the dignity and respect of the Prophet of Islam, He has permitted needy seyyeds or Banu Hashim (those whose lineage reaches Hashim, the grandfather of the Prophet) to receive charity through Khums only. Thus, Allah put their share on a par with His share and that of the Prophet so as to do away with what may cause their degradation.
3. Khums is to meet the expenses of every charitable work or such purposes to which the Imam (a.s.) consents.
4. Khums is considered to be a means for human growth and perfection. It is the key to sustenance and forgiveness of sins.
5. Khums has been made obligatory to help revive the religion of God and actualize the Islamic government.
Consumption of Khums
Khums is given to the Imam and Sadaat. During the present time, the era of occultation, it should be given to a qualified Mujtahid. In answer to the above two questions, the verdicts of grand jurists are as under:
Imam Khomeini (r.a): He must pay it to the Marja whom he follows or to a Mujtahid who spends on the same purpose in quality and quantity as required by the Mujtahid whose Muqallid the payer is.
Grand Ayatollah Khamenei: Khums should be given to the guardian of Muslims' affairs or to his authorized representative, and if he acts according to the fatwa of the Mujtahid whom he follows, he will be relieved of obligation.
Grand Ayatollah Fazel Lankarani (r.a), Ayatollah Noori Hamedani, Ayatollah Makarem Shirazi, Ayatollah Bahjat and Ayatollah Wahid Khurasani: He must pay it to the Marja whom he follows or to a Mujtahid who spends it on the same purpose in quality and quantity as required by the Mujtahid whose Muqallid the payer is, or it should be spent on such purposes as allowed by that Mujtahid. Sahme Sadat should be given, as an obligatory precaution, to the Marja whom he follows or be given to poor Seyyeds with the permission of the Mujtahid.
Grand Ayatollah Tabrizi: Sahme Imam (a.s.) should be given to the Mujtahid whom he follows or be spent for such purposes as allowed by the Mujtahid. And if one wishes to give Sehme Imam to a Mujtahid whom he is not following, he can give it with the permission of the Mujtahid whom he is a Muqallid of. As for Sahme Sadat, he himself can give it to poor Seyyeds.
Grand Ayatollah Sistani: During the present time it should be given to a Mujtahid, who fulfils all conditions, or be spent for such purposes as allowed by that Mujtahid. As an obligatory precaution, that Mujtahid must be Aalam, and well versed in public affairs. As for Sahme Imam, it can be given to the Seyyeds themselves.
Grand Ayatollah Saafi: He must pay it to the Marja whom he follows or to a Mujtahid who spends on the same purpose in quality and quantity as required by the Mujtahid whose Muqallid the payer is, or it should be spent for such purposes as allowed by his Marja. And Sahme Sadat can be given to the Seyyeds themselves.
Note: Khums should be divided into two parts. One part is Sahme (share of) Imam (a.s.), and the other is Sahme Sadat. When it comes to paying Sahme Sadat, Grand jurists such as Sistani, Tabrizi (r.a) and Saafi do not consider the Mujtahid's permission to be necessary; [thus, he can pay it to poor and faithful Seyyeds without obtaining their permission.]
 - Tawzih al-Masail of Maraje', vol.2, issue 1834
 - Khamenei, Ajwebat al-Masail (Answers to Religious Enquiries), question 1002 and 1004.
 - Tawzih al-Masail of Maraje', vol.2, issue 1834; Noori, Tawzih al-Masail, issue 1830; Wahid, Tawzih al-Masail, issue 1843.
 - Tawzih al-Masail of Maraje', vol.2, issue 1834.
 - Ibid.
 - Ibid.