“Eid Mubarak!” The Muslim holiday Eid al-Adha officially began Monday and continues through Thursday. It's also known as the Feast of Sacrifice or the Greater Eid and is held in observance of the biblical story of Abraham’s sacrifice to God.

Eid al-Adha marks the end of Hajj, one of the largest religious gatherings that requires Muslims to embark on a major pilgrimage to Mecca. Muslims greet each other using the most common term, “Eid Mubarak,” or “Blessed Eid.”

Eid al-Adha typically begins with morning prayers and celebrations involving visiting with friends and family. Historically, the holiday involves animal sacrifices, or a “qurbani.” For those who can afford it, animals – typically a cow, sheep or goat – are slaughtered and the meat is divided and distributed to the poor.

The ritualistic slaughter is done to commemorate the story of Abraham, who was asked by God in a dream to sacrifice his son as an act of obedience. As Abraham was about to act, God instead bestowed upon him a sheep to kill in his son’s place. Versions of the story appear in the Bible’s Old Testament.

Many Muslims will also donate to charities and gifts are exchanged during the holiday.

The Eid-al-Adha festival is dependent upon the sighting of the new moon. Because of this, Muslims in some countries may not celebrate the holiday until Tuesday.

Eid al-Adha is the second of two major holidays in the Islamic religion. The other is another Eid holiday called Eid al-Fitr, which is a holiday that is celebrated following the end of the Ramadan month of fasting.

RTSNBQA A butcher slaughters a sacrifice goat during Eid al-Adha near a mosque in Bangkok, Thailand Sept. 12, 2016. Photo: REUTERS/Athit Perawongmetha

RTSNBV1 Muslim pilgrims shave their heads after they cast stones at pillars symbolizing Satan, during the annual Hajj pilgrimage on the first day of Eid al-Adha in Mina, near the holy city of Mecca, Saudi Arabia Sept. 12, 2016. Photo: REUTERS/Ahmed Jadallah

RTSNC1C Men put out freshly slaughtered goat and cow meat for donation to the poor during Eid al-Adha festival near a mosque in Jakarta, Indonesia Sept. 12, 2016. Photo: REUTERS/Iqro Rinaldi

RTSNC2W Muslims attend an Eid al-Adha mass prayer marking the end of the annual Hajj pilgrimage, in Mombasa, Kenya Sept. 12, 2016. Photo: REUTERS/Joseph Okanga

RTSNC7V A woman gives water to a goat at her house after purchasing it at a livestock market on the eve of the Eid al-Adha festival in Kolkata, India Sept. 12, 2016. Photo: REUTERS/Rupak De Chowdhuri

RTSNCQ5 Muslims attend an Eid al-Adha mass prayer marking the end of the hajj pilgrimage in Somalia's capital Mogadishu, Sept. 12, 2016. Photo: REUTERS/Feisal Omar

RTSNBGR Palestinians slaughter a calf during the Muslim festival of Eid al-Adha in Khan Younis in the southern Gaza Strip Sept. 12, 2016. Photo: REUTERS/Ibraheem Abu Mustafa

RTSNBNZ Muslim pilgrims walk on roads as they head to cast stones at pillars symbolizing Satan during the annual hajj pilgrimage in Mina on the first day of Eid al-Adha, near the holy city of Mecca, Saudi Arabia Sept. 12, 2016. Photo: REUTERS/Ahmed Jadallah TPX IMAGES OF THE DAY

RTSNBON Butchers slaughter sacrifice goats during Eid al-Adha near a mosque in Bangkok, Thailand Sept. 12, 2016. Photo: REUTERS/Athit Perawongmetha

RTSNBPZ Butchers slaughter sacrifice goats during Eid al-Adha near a mosque in Bangkok, Thailand Sept. 12, 2016. Photo: REUTERS/Athit Perawongmetha