Knights of the Round Table

The general term for the knights who left their names in King Arthur's legend. They are called the Knight of the Round Table because they gathered around a round table along with King Arthur. The knights sitting around the table were all regarded as equal to one another, including the King himself, and they were admired throughout the country. Though the number of them varies according to each story, the standard pattern of thirteen knights is accepted in Fate/stay night.
In the Apocrypha world, the separate splinters from the Round Table serve as summoning catalysts for Heroic Spirits. From among eleven of the knights (with King Arthur and Galahad excluded), the one most compatible to the Master is summoned through it. Like an S-rare definite ticket. Whether it be someone like Lancelot, Gawain, Tristan or Percival, no matter who comes, you truly get the cream of the crop. During these current times where subspecies Holy Grail Wars are popular, they appear in the market at high prices. Naturally, there are many frauds and swindlers. It'd be nice if a certain oil magnate got swindled.

Fate/Apocrypha material: Fate/Apocrypha Encylopedia