baseball card dimensions
 

Does your definition of a baseball card include a minimum or maximum height, width, or thickness? Do the surfaces have to be rectangular? I personally would be okay considering a disk of 1 mm² or 10 ft² a baseball card as long as it met the other criteria, but I feel like a baseball card does at least have to be a card. That said, I do actually collect 1946-47 Propaganda Montiels, which look a heckuva lot like baseball cards, but once you've held one you know they aren't actually cards at all, since they're only about as thick as a Bible page.

Probably for many of us, it's in line with this famous assessment:

"I can't define what pornography a baseball cards is, but I know it when I see it."

I would propose: A baseball card is a stand-alone item on cardboard, featuring a baseball related image, in which that image is the primary component of the item, and can be effectively handled in stacks.

A magazine, book cover, or 6 foot tall life size stand-up of a baseball player are not cards. A poster is not a card. It need not be in the traditional rectangle shape that most are. A playing card, a Bond Bread, a postcard are all cards.

There are baseball cards, then there is the baseball card "genre." The latter includes closely related non-card things such as Armour Coins, S72 silks, Topps Stamps, Domino Disks etc.