From the Comprehensive Rules:
108.2. When a rule or text on a card refers to a "card," it means only a Magic card or an object represented by a Magic card.
108.2a. Most Magic games use only traditional Magic cards, which measure approximately 2.5 inches (6.3 cm) by 3.5 inches (8.8 cm). Traditional Magic cards are included in players' decks. Certain formats also use nontraditional Magic cards. Nontraditional Magic cards are not included in players' decks. They may be used in supplementary decks. Additionally, they may be oversized, have different card backs, or both.
108.2b. Tokens aren't considered cards--even a card-sized game supplement that represents a token isn't considered a card for rules purposes.