Infinity isn't a real resource symbol. Infinity is like the "wild card" of the resource symbols. When a card with the Infinity resource symbol is played, the player chooses what Infinity will represent.

One of the most notable uses for cards with the Infinity symbol is the character card The Universal Fighter, since it provides a defense against cards which restrict block cards with certain resource symbols, such as Soul Power, Troubled Orphan, or Shiranui Ninja Arts.