In Islam there are two Eid's or celebrations. The first Eid is Eid al-Fitr. This one is celebrated to mark the end of the holy month of Ramadan. The next Eid , is Eid al-Adha and this one is celebrated usually at the end of the Hajj Pilgrimage. The Hajj Pilgrimage is obligatory act on all Muslims who are healthy and able. It is one of the pillars in Islam.
For the two Eids the day of celebration is dependent on the sighting of the moon. This is because Muslims follow a lunar calendar. Eid al-Adha is celebrated in the last month (twelfth) of the Islamic calendar and is commemorated in celebration of Ibrahim's (Abraham's) willingness and devotion to follow the commands of God and sacrifice his son Ismail (Ishmael). In his stead God places a ram for sacrifice. So on this day Muslims sacrifice sheep, goats, lambs, and the like. The meat of the animal is then distributed to friends, family, and charity.