It can refer to many types of cards, like:
* A credit card: "Tengo una tarjeta de crédito." (I have a credit card.)
* A business card: "Aquí tienes mi tarjeta de presentación." (Here's my business card.)
* A playing card: "Sacó una tarjeta de la baraja." (He drew a card from the deck.)
* A greeting card: "Le envié una tarjeta de felicitación." (I sent her a greeting card.)
The specific type of card will be determined by the context of the sentence.