From The Dim Future Wiki
The subtype is a set of descriptive words that apply to the card. The card is considered to have each word as a separate subtype, so a card that says "Character - Snake Mage Female" would have three subtypes: "Snake", "Mage" and "Female". They do not make any difference to the effect or usage of the card, however other cards can effect cards with different subtypes differently. If a card asks for or effects "Human" cards, all cards with "Human" as a subtype are effected.