If you read the text on Kith's Khymeramasters, it mentions a Khymera Token. I would guess that token cards are cards brought out by other cards. Such cards are common in e.g. Magic the Gathering and Hearthstone.
Good catch Magnus! Well that's interesting. That's certainly something different coming from the FFG design house. Not saying that it's original, but I'm certainly very interested in how it is implemented in this game. Seems like having 40 of the token cards in the game mean they are probably important somewhat. Interesting how they didn't reveal any in the previews just yet.