Celebrated about two months after Aidilfitri, on the 10th day of Zulhijah, the 12th month of the Muslim calendar, it marks the end of the haj pilgrimage period (about two weeks); hence the name Hari Raya Haji (festival of the pilgrimage).
Every year millions of Muslims make the journey to the Holy Land of Mecca in Saudi Arabia to perform the haj, a requirement in Islam as it makes up one of the five tenets of the religion. As long as they have the means to do so, and are able health-wise, Muslims must perform the haj at least once in life. Upon completion of the haj, the men earn the title of "haji" and the women, "hajjah".
Aidiladha also commemorates the sacrifices made by the prophet Abraham (hence the word "korban" which means sacrifice), who demonstrated immense faith when he was put to the test by God. The prophet was commanded to offer his only son Ishmael up for sacrifice, and though it grieved him greatly, he made ready to perform the task. However, as he was about to strike his son, God stopped him and revealed that it was a trial. Ishmael's life was spared, and a ram sacrificed in his place.
As such, during Aidiladha, the sacrifice of animals such as lambs, goats, cows, bulls and camels is performed. The animals are slain in accordance with the proper religious rites; the meat is then distributed.
One third of the meat is given to the individual who willingly supplied the animal, while the rest is given to the poor and deserving friends and relatives. It is to be noted that this is not a compulsory religious duty, but an obligation for those who are able to afford it.
The observance of the korban is carried out after the congregational prayers, held early in the morning of Aidiladha. It is not unusual for the slaying to take place within the mosque compound.
The rest of the day is either spent visiting friends and relatives, or entertaining guests at home, as is customary in this multicultural country.
Though in Malaysia the celebration of Aidiladha is relatively solemn compared to Aidilfitri, by no means is it less important, for it is a day when Muslims reaffirm their faith in God, giving thanks for the many blessings that He has bequeathed to them.
source from: http://allmalaysia.info/msiaknow/festivals/rayahaji.asp