Tokens are cards that don't exist in your Deck, but instead are created through unit summons or stat boosts. There are two types of Tokens: Unit Tokens and Stat Tokens.
Unit Tokens are Mana-based summons. They are X/Y Unit summons (where X is Attack and Y is Health) that aren't Beings or Structures. Unit Tokens can't manifest like Anima, nor build Structures like Tamers. They have 0 Dexterity and 1 Mobility by default.
Stat Tokens include Health, Attack, Mobility, Dexterity Tokens. They are placed under Units to boost Statistics.