the Holy Grail is the name given in medieval legends of chivalry to the chalice used by Our Lord at the Last Supper, from which all the apostles first drank the Precious Blood. Associated with the grail in these legends, which involve seeking and finding and great trials of strength and courage, is the krater, the plate used for the bread, the Body of Christ, and usually the head of the lance that pierced the side of Christ.
the name became a literary reference to any device in one of these “seeking” stories that represented a relic of Jesus, or any mundane object made sacred by association with Christ. the symbolism behind these stories is the requirement of purity of mind, heart and body as the prerequisite for finding the object and through it, finding God or becoming closely united with Jesus Christ. On a deeper level, these stories were allegories of the spiritual life.
No one knows where these actual objects are, any more than they know where to find the Ark of the Covenant, which is why they make excellent topics for adventure stories, now as in the middle ages.