"Lord Buddha's Parinirvana," also known as Mahaparinirvana, signifies the final and ultimate passing away of Siddhartha Gautama, the historical Buddha and the founder of Buddhism. This momentous event signifies the conclusion of his physical existence and his attainment of Nirvana, the highest state of liberation from suffering and the cycle of birth and death, as per Buddhist belief. Traditionally, the Parinirvana of the Buddha is said to have transpired on the full moon day during the month of Vaishaka, usually falling in April or May, in the year 483 BCE, according to the Theravada tradition. Nevertheless, it's worth noting that various Buddhist traditions may observe slightly different dates for this significant occurrence.