What is Eid Milad un Nabi ?

Eid e milad milad in nabi or Mawlid means "Birth of the Prophet".
It is the observance of the birthday of the Prophet Mohammed(sallahu tala alehiwasallam) which occurs on the 12th day of Rabi' al-awwal, the third month in the Islamic calendar.
It day Celebrated by Sunni Muslims or People who love Mohammed(S.A.W) through out the world.

On this day Muslims fast and pray to Allah as well as bring out large procession to mark this day.

Even Prophet Mohammed(S.A.W) celebrated this day by fasting.

This day is very important for Muslims as Mohammed(S.A.W) has born this day.

In India and in many countries this day is declared as national holiday.

Other Names used to Describe this day :

Eid al-Mawlid an-Nabawī – Festival of the birth of the Prophet (Arabic)
Eid-e-Milād-un-Nabī – Festival of the birth of the Prophet (Urdu)
Eid-e-Meeladun Nabi – The Birth of the Prophet (Bangladesh, Sri Lanka, Maldives, South India)
el Mūled (en-Nabawi)/Mūled en-Nabi – The birth (of the prophet )/Birth of the prophet (Egyptian Arabic)
el Mūled - The birth (Tunisian Arabic)
Gamou – ? (Wolof)
Mawlûd – Birth of the Prophet صلى الله عليه وسلم (Arabic)
Mawlid an-Nabī (pl. al-Mawālid) – The Birth of the Prophet (Arabic)
Milād an-Nabī – The Birth of the Prophet (Urdu)
Maulidur-Rasūl – The Birth of the Messenger of Allah (Malay)
Maulid Nabi – The Birth of the Prophet (Indonesian)
Maulud Nabi – The Birth of the Prophet (Malaysian)
Maulidi – The Birth of the Prophet (Swahili, Hausa)
Mawlūd-e Sharīf – The Blessed Birth (Dari/Urdu)
Mawlid en-Nabaoui Echarif – The Blessed Birth of the Prophet (Algerian)
Mevlid-i Şerif – The Blessed Birth / Mevlüt – The Name (Turkish)
Mevlud/Mevlid – The Blessed Birth (Bosnian)
Mevlydi – The Blessed Birth (Albanian)
Milād-e Payambar-e Akram – The birth of the great/blessed Prophet (Persian)
Mulud – The Birth (Javanese)
Nabi/Mahanabi Jayanti – The birth of the (great) Prophet (Sanskrit, South Indian Languages). Maha means "great."
Yawm an-Nabī – The Day of the Prophet (Arabic)