Wesak Day is a Holy Day for Buddhists. In fact, it is considered the holiest day in the Buddhist Calendar.
The Buddha's birthday is observed annually on the Sunday nearest to the full moon in May. It is a holiday observed by Buddhists across the world, though the exact date may differ from country to country.
In Malaysia, Wesak Day is also considered one of the country's major festivals.
In Indonesia, the holiday is known as Waisak Day.
Besides being the time of the year when Buddhist temples sport a beautiful display of lights, it is also the time when Buddhists spend the whole sacred day at temples meditating, chanting prayers and offering alms to Buddhist monks.
An example of the celebrations at a temple during Wesak Day is the Vihara Temple at Brickfields, Kuala Lumpur. The celebrations start at sunrise when devotees gather at the temples to meditate. In the evening, a candlelight procession from the temple to Kuala Lumpur city takes place. Many thousands of Buddhists and spectators line the route of the procession, which is led by a decorated float with a statue of the Buddha in it.
After the procession returns to the temple, a special open-air blessing service is performed and a sermon on the significance of Wesak Day is held. Traditionally the rest of the night is spent with devoted meditating, chanting and offering prayers to Lord Buddha by monks in saffron robes.
To summarise, Wesak is important because it marks three key events in Lord Gautama Buddha's life - his birthday, the enlightenment and his achievement of Nirvana.