Adha, a period of "communal enjoyment" for Muslims worldwide, has officially arrived. Here's what we've learned about the Islamic holiday.

Large numbers of Muslims converge once a year on Saudi Arabia to unite in a series of religious rituals and acts of worship as they perform the Hajj, the pilgrimage that is one of the pillars of Islam.

On Friday Muslims will begin observing Eid al-Adha, a time for prayer and charity. The religious festival occurs over three to four days and is one of the major Islamic celebrations observed by Muslims every year.