Eid al-Adha is the second Islamic festival of the year and follows Eid al-Fitr, which marks the end of Ramadan, the holy month of fasting. The date changes every year, as it's based on the Islamic lunar calendar.
The holy festival of Eid-ul-Zuha, also known as the 'festival of sacrifice' or Greater Eid, is celebrated on the 10th day of Dhu al-Hijjah, the 12th month of the Islamic or lunar calendar.