Short answers, pulled from the story.
As of 2020, there are approximately 320 million Buddhists worldwide, representing about 4.1% of the global population. Earlier estimates placed the figure around 500 million, but those counts were complicated by religious syncretism in China and Japan, where distinguishing active practitioners from cultural adherents is difficult.
Thailand has the largest absolute number of Buddhists, estimated at 67 million. Japan follows with around 45 million, and Myanmar has approximately 38 million.
The earliest recorded usage of the word Buddhist in English dates to 1810. The term was formed by combining Buddha with the suffix -ist, denoting an adherent of a belief system.
The two largest traditions are Theravada Buddhism, predominant in Sri Lanka, Thailand, Myanmar, Cambodia, and Laos, and Mahayana Buddhism, dominant in China, Japan, Korea, and Vietnam. A third major tradition, Vajrayana, is found mainly in Tibet, Bhutan, and Mongolia.
According to the Pew Research Center, Buddhists were the only major religious group to shrink in absolute size between 2010 and 2020, dropping from about 343 million to roughly 324 million. The decline is driven by an aging population, low birth rates, and rising irreligion in East Asian countries.
Vesak, also known as Buddha Day or Buddha Purnima, is the most widely observed Buddhist festival across all traditions. Held on the full moon of the month of Vaisakha in April or May, it commemorates the birth, enlightenment, and passing into Nirvana of Siddhartha Gautama.