BAITUL MAL OR BAYT AL-MAAL
The literal meaning of the Arabic term ‘Bayt al Maal’ means the ‘House of Treasury’ or the House for Money, ie. the ‘Central Treasury’ which an Islamic State establishes to hold the wealth of the nation. It is from this ‘Bayt al Maal’ or Central Treasury whereby all the zakah, sadaqah, jizya, etc. dues are collected and spent on the running of the state and the spending on the poor and the needy.It is clear that attainment of socio-economic justice is an immediate objective of the Bayt al-Maal. The Bayt al-Maal bears the responsibility of the undertaking of the society's fiscal(Economic) system and welfare provisions. 
And what Allah restored to His Messenger from the people of the towns - it is for Allah and for the Messenger and for [his] near relatives and orphans and the [stranded] traveler - so that it will not be a perpetual distribution among the rich from among you. Quran Surah Hashr 59:7
The name Bait-ul-mal was chosen because of its significance as a financial institution in Islam.
Prophet Muhammadﷺ, established the common brotherhood of Muslims soon after the Hijrah (migration) to Medina from Makkah. Each resident of Medina became a helper (ansar) to each individual who migrated with Prophet Muhammadﷺ. The rich Muslims took charge of the poor ones and soon the economic disparity was removed with the interdependency.
Prophet Muhammadﷺstarted the Bait ul Mal (a central financial treasury) after the battle of Badr and the first Mosque, Masjid-e-Nabi (Mosque of Prophet Muhammad), which served as the center of collection and distribution for zakat (charitable tax) and sadaqa (additional contributions).
During the time of Khalif Umar, the Bait ul Mal became larger and it played the role of the Public Exchequer for the entire Islamic State. Umar then invented the new system of salary and welfare, etc. For example, the poor or unemployed, could get an amount of money from the Bait ul Mal. Even women, who were either pregnant or nursing and had no one else to take care of them, received a monthly stipend from the Bait ul Mal.