Size-wise what is considered a 'card'?

[poorlydrawncat]

Just the other day I stumbled on a post in the baseball card subreddit (reddit.com/r/baseballcards) by someone who had found a stash of R312s in his grandfathers basement. He thought they were blank postcards or just colored photographs. I think laymen generally have a stricter conception of baseball cards that only include cards of certain sizes and aesthetics. So if you go by the common definition of the term, then no, I don't think they'd be considered baseball cards. In the collector's circle on the other hand, "baseball cards" is more of an umbrella term which it seems to me generally does include things like exhibits, premiums, etc. I really think it depends on the context in which the word is spoken.