Full moon days in Hindu calendar are known as Purnima or Pournami.
South Indian people called it as Pournami, whereas North Indians called it as Purnima.
Vaisakham is the second month in Hindu calendar.
Apart from festivals, Pournami is a very important and auspicious day in Hindu calendar. Pournami that falls in the month of Vaisakha is called as Vaisakha Purnima or Vaisakha Pournami or Baisakhi Pournami.
Budha Jayanthi is celebrated on Vaisakha Purnima day, as this day is birth anniversary of Gautama Budha. The day is also called as Budha Purnima.