BAITU ‘L-MAL بيت المال.
Lit. “The House of Property.” The public treasury of a Muslim state, which the ruler is not allowed to use for his personal expenses, but only for the public good.
The sources of income are: (1) Zakat, or the legal tax raised upon land, personal property, and merchandise, which, after deducting the expense of collecting, should be expended in the support of the poor and destitute. (2) The fifth of all spoils and booty taken in war. (3) The produce of mines and of treasure-trove (4) Property for which there is no owner. (5) The Jizyah, or tax levied on unbelievers. (Hidayah, Arabic ed. vol i. p. 452.)
Based on Hughes, Dictionary of Islam