Eid al-Fitr or “Festival of Breaking the Fast”, is a religious holiday celebrated by Muslims worldwide that marks the end of the month-long dawn-to-sunset fasting of Ramadan. This religious Eid is the only day in the month of Shawwal during which Muslims are not permitted to fast. The date for the start of any lunar Hijri month varies based on when the new moon is sighted by local religious authorities, so the day of celebration varies by locality.

The date of Eid al-Fitr depends on the lunar calendar, which is why it falls on a different date on the Gregorian calendar on an annual basis.

The festival is a day when Muslims thank Allah for strength and blessings, hoping the commemoration of Ramadan has brought them closer to god.

It was first celebrated by Muhammad in 624CE following a victory in battle.

https://en.wikipedia.org/wiki/Eid_al-Fitr

https://www.independent.co.uk/life-style/eid-al-fitr-when-ramadan-mubarak-meaning-definition-holiday-islam-a8941211.html