Today (Friday, May 24) marks one of the most important Buddhist holidays. Vesak, otherwise known as “Buddha Day” (or sometimes “Buddha’s Birthday”) commemorates the birth, enlightenment, and death of Siddhartha Gautama, the historical Buddha.

Although observed by Buddhists in many lands, Vesak is a holiday of particular significance among Theravada Buddhists, adherents of the branch of the religion most common throughout Sri Lanka, Myanmar (Burma), Laos, Cambodia, and Thailand.

The name of the holiday is derived from Vesakha, the name of the current month in the Pali language of the traditional Theravada Buddhist calendar (Pali being related to Sanskrit and the language of the Pali Canon, the scriptures of Theravada Buddhism). Vesak is celebrated upon the first full moon of that month.

Because this calendar is a lunar calendar, there is a certain amount of built-in “drift” with regard to corresponding dates on the Western (Gregorian) calendar, which means that Vesak does not always fall on the same Western calendar date. Last year, for instance, Vesak was celebrated on May 5, 2012 in most countries (there is some regional variation); next year, by contrast, it is anticipated to fall upon May 13, 2014.

Vesak is traditionally observed with special temple ceremonies, hymns, offerings, sermons, giving to charity, vows and rededication, and of course vegetarian feasts. One popular practice associated with the holiday is the ceremonial washing or bathing of small figures of the baby Buddha, a rite of symbolic cleansing.