What is "vesak"

Vesākha ( Pali; ), also known as Buddha Purnima and Buddha Day, is a holiday observed traditionally by Buddhists on different days in India, Sri Lanka, Nepal, Tibet, Bangladesh, Bhutan, Indonesia, Philippines, Singapore, Vietnam, Thailand, Cambodia, Laos, Malaysia and Myanmar and in other places all over the world. Sometimes informally called " Buddha's Birthday", it actually commemorates the birth, enlightenment ( nirvāna), and death ( Parinirvāna) of Gautama Buddha in the Theravada or southern tradition.