Eid ul Fitr marks the end of the holy period of Ramadan and the beginning of Shawwal, the tenth Islamic month. On Eid ul Fitr (also known as Eid al-Fitr or Id ul-Fitr), Muslims thank Allah for the holy Quran.
The sacred book of the Muslims was revealed to Prophet Muhammed on Laylat al-Qadr, one of the odd-numbered nights during the last ten days of Ramadan. Hence the significance. And moreover, fasting (Sawm) is one of the Five Pillars of Islam, and therefore Muslims fast during the holy month of Ramadan.