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Explanation: As the other two translators have suggested, there are several translations for this word depending on the context. All the translations given are widely used, there may be other options if you ask people from other countries where Spanish is spoken.
When playing cards, it is "carta".
When it refers to a birthday card, it is "tarjeta de cumpleaños".
If it is just a card you send when you are on holidays, in Spain, you would say "una (tarjeta) postal".
If it is a Christmas card, you say "un Christmas", "postales navideñas", "tarjetas de Navidad"...
If you are talking about a "business card", you would use "tarjeta de visita".