In Parzival, the grail (or "Gral" as it is spelt), is a thing that magically serves men whatever they desire. On Parzival's first visit to the grail castle, it is brought in by a Princess:

Her face shed such refulgence that all imagined it was sunrise, This maiden was seen wearing brocade of Araby. Upon a green achmardi she bore the consummation of heart's desire, its root and its blossoming - a thing called "The Gral", paradisal, transcending all earthly perfection! She whom the Gral suffered to carry itself had the name of Repanse de Schoye. Such was the nature of the Gral that she who had the care o f ti was require to be of perfect chastity and to have renounced all things false. (124)
As the knights sit down to eat, the magical properties of the grail become evident:
Now I have been told and I am telling you on the oath of each single one of you - so that if I am deceiving anyone you must all be lying with me - that whatever one stretched out one's hand for in the presence of the Gral, it was waiting, one found it all ready and to hand - dishes warm, dishes cold, new-fangled dishes and old favorites, the meat of beasts both tame and wild .... (126)
Later on, Parzival learns more about about the powers of the grail. The grail is guarded by a company of knights called the Templars:
They live from a Stone whose essence if most pure .... Further: however ill a mortal may be, from the day on which he sees the Stoen he cannot die for that week , nor does he lose his color. For if anyone, maid or man, were to look at the Gral for two hundred years, you would have to admit that his color was as fresh as in his early prime .... This Stone is also called "The Gral". (239)
Another property about the grail is that it can only be seen by Christians. When Feirefiz, Parzival's heathen half-brother is in the presence of the grail, he cannot see it. But after he is baptized into the faith, "the Gral was unveiled to his vision" (406).

Selections from Wolfram von Eschenbach's Parzival. Translated by A.T. Hatto