"Maghapuja" is a Pali (and Sanskrit) word consisting of two elements - Magha and puja, which mean "the third lunar month" and "worship" respectively. So, the whole word means " worship on the full-moon day of the third lunar month in commemoration of the Great Assembly of Disciples".

According to Buddhist scriptures, nine months after Siddhartha Gautama attained enlightenment, on the full-moon day of the third lunar month corresponding to the zodiacal sign of capricornus, in the year 44 before the Buddhist Era, or 587 B.V., a total of 1,250 disciples of the Buddha from various places spontaneously assembled at Wat Veluvan in Magadha to pay their respects to their Teacher. This meeting is considered very significant in Buddhist history because first, it was done without previous appointment and was therefore a miracle, and secondly, all the disciples had been ordanied by the Buddha himself and had attained sainthood and become Arahants.