What are "game key cards?"

Is it a physical card? Is it just a piece of paper with the download code? I can't find a straight forward answer anywhere. I understand you have to download the game but I don't understand is if they just give you a fake card that you'll have to pop in to still play. Does the card even have a cover image?

Nintendo systems are the only ones I care about getting games physical. mainly because I want to save on download space and also the nostalgia of taking out the old game and popping in a new one.

Currently Persona 3 Reloaded is $39 on Amazon "game key card" while on the eShop it's $59 which is the game I'm meaning to get.