It’s a soggy piece of cardboard that “they” give you at birth and you have to hold onto it with your tiny baby hand, and then you have to keep it until you’re like 90 years old. If this soggy, easy to lose or destroy card gets lost or destroyed you have to prove to the magically animated statue of Abraham Lincoln himself that you’re American to get a replacement.
This card is explicitly not an ID card, but the only thing it ever gets used for is as an ID card.