Diwali

Diwali, or Dipawali, is India's biggest and most important holiday of the year. The festival gets its name from the row (avali) of clay lamps (deepa) that Indians light outside their homes to symbolize the inner light that protects from spiritual darkness. This festival is as important to Hindus as the Christmas holiday is to Christians.

Over the centuries, Diwali has become a national festival that is enjoyed by most Indians regardless of faith: Hindus, Jains, Buddhists, and Sikhs.

Hindus interpret the Diwali story based upon where they live:

In northern India they celebrate the story of King Rama's return to Ayodhya after he defeated Ravana by lighting rows of clay lamps.
Southern India celebrates it as the day that Lord Krishna defeated the demon Narakasura.
In western India the festival marks the day that Lord Vishnu, the Preserver (one of the main gods of the Hindu trinity) sent the demon King Bali to rule the nether world.

In all interpretations, one common thread rings true—the festival marks the victory of good over evil.

Non-Hindu communities have other reasons for celebrating the holiday:

In Jainism, it marks the nirvana or spiritual awakening of Lord Mahavira on October 15, 527 B.C.
In Sikhism it marks the day that Guru Hargobind Ji, the Sixth Sikh Guru was freed from imprisonment.