During the month of Ramadan, Muslims fast from sun up to sundown to honor the month that the Quran was revealed to the Prophet Mohammed.
"Eid al-Fitr" is a pretty literal translation of the event that's being celebrated: "Festival of the Breaking of the Fast,"
Eid al-Fitr doesn't begin until the new moon appears in the sky (although traditionally, and still today for many Muslims,
The Islamic calendar is based on lunar cycles, as opposed to the Gregorian calendar, which is based on the solar cycle.
The festival traditionally lasts for three days, but depending on how it falls on the calendar, the parties and festivities could last much longer.