The Holy Moon Cálice was an item belonging to Sailor Moon which had different origins and functions in the anime and manga.
In the anime, the Holy Moon Cálice was never discussed or given a name. It first appeared in episode 187 after Sailor Chibi Chibi Moon gave Eternal Sailor Moon the power up which allowed her to perform Silver Moon Crystal Power Kiss.
At the beginning of Eternal Sailor Moon's Silver Moon Crystal Power Kiss attack sequence, this item appeared and attached to the bottom of the Eternal Tiare. The Tiare then extended out from the bottom of the Cálice, and the lengthened Tiare was called the Moon Power Tiare.
The name "Holy Moon Cálice" comes from the toy replica produced by Bandai; in the manga, it was still called "Holy Grail" (聖杯).