This is the Blank Business Card developed by Toronto artist Dorota Pankowska. The card consists of three separate layers of cardstock glued together, the middle of which is a laser cut stencil that reveals the card's information when viewed in front of a bright light. Interesting. These would be perfect for...actually I'm not sure who these would be perfect for. *gets handed business card* What the hell is wrong with you, this is blank. "Hold it up in front of a bright light." What are you, trying to blind me? This is going to be like that whole eclipse thing all over again.
Keep going for one more shot of a card without the top layer added just in case you're really struggling with this idea because you were kidnapped by mole people and have been living underground for a year and forgot how light works (it happens).
Thanks to Cyndi M, who agrees the best business card isn't a card at all, it's making a first impression so great that the person immediately puts your number in their phone along with your picture and makes your name 'AAA+ PERSON, MUST HIRE'.