What's a "Grail"?
Simply put, a "Grail" in the Funko Pop! community is one of significant value that has been vaulted (retired from the market).
In the FigPin community, a "Grail" is one of rarity.
Although these are frequent ways used to define a grail, the true meaning of a grail to a collector is an item that you ADORE and consider a must have.