Ullambana Sutra; Yulanpen Sutra
A Buddhist sutra associated with the Obon festival and the story of Mokuren (Maudgalyāyana) saving his mother from the realm of hungry ghosts. The title is a proper noun referring to a specific scripture.
The Ullambana Sutra is a sutra considered to be the origin of the Obon festival.
お盆 is the Japanese Buddhist custom to honor the spirits of ancestors, while 盂蘭盆経 is the specific sutra that provides the scriptural basis for the festival.
From Chinese 盂蘭盆經 (Yúlánpén jīng), itself a transliteration of Sanskrit 'ullambana' (hanging upside down, a metaphor for suffering) combined with 経 (sutra).