This Thursday June 3rd is 'Buddha Day' (also known as Vesak or Visakah Puja).
"There are many special or holy days held throughout the year by the
Buddhist community. Many of these days celebrate the birthdays of
Bodhisattvas in the Mahayana tradition or other significant dates in
the Buddhist calendar. The most significant celebration happens every
May on the night of the full moon, when Buddhist all over the world
celebrate the birth, enlightenment and death of the Buddha over 2,500
years ago. It has become to be known as Buddha Day."
"Traditionally, Buddha's Birthday is known as Vesak or Visakah Puja
(Buddha's Birthday Celebrations). Vesak is the major Buddhist festival
of the year as it celebrates the birth, enlightenment and death of the
Buddha on the one day, the first full moon day in May, except in a
leap year when the festival is held in June. This celebration is
called Vesak being the name of the month in the Indian calendar."
buddhist mahayana festivals
I hope this answers your question, if you require any clarification,
please do not hesitate to ask.