What is Eid ul-Fitr?
Eid ul-Fitr marks the end of Ramadan. It falls on the 1st of Shawwāl. It is a day of gratitude to Allah for the strength to complete the fast, and a celebration of the spiritual growth gained during the month.
The one who fasts has two joys: joy when he breaks his fast, and joy when he meets his Lord.
Sahih al-Bukhari · Sahih Muslim
Note: Fasting on Eid day is ḥarām (prohibited).