The Holy Grail is a legendary and mysterious object that has been the subject of many stories and myths throughout history. It is said to be a cup or dish that was used by Jesus at the Last Supper, and is believed to possess miraculous powers. It has been sought after by many people
From Wikipedia
The Holy Grail is a treasure that serves as an important motif in Arthurian literature. Various traditions describe the Holy Grail as a cup, dish, or stone with miraculous healing powers, sometimes providing eternal youth or sustenance in infinite abundance, often guarded in the custody of the Fisher King and located in the hidden Grail castle. By analogy, any elusive object or goal of great significance may be perceived as a "holy grail" by those seeking such.