The Sikh Holiday of Vaisakhi is celebrated every year on April 14. Also frequently spelled Baisakhi, Vaisakhi has origins as a springtime festival in the Punjab region, but since 1699 has taken on a great deal of religious significance for Sikhs. On Vaisakhi in that year, Guru Gobind Singh created the Khalsa and established much of what is at the core of the Sikh faith today.
For a thorough explanation of Vaisakhi's significance and origins, read HuffPost blogger Satpal Singh's post, Vaisakhi: Sikhs Celebrate Life, Liberty, and the Pursuit of Happiness.
Indians observe Vaisakhi by making pilgrimages and participating in rituals at traditional holy sites. Dancing, fireworks, and feasts among family and friends are also common practice for those in India, Pakistan, and around the world.