Today, flat or folded can be used interchangeably.  Traditionally, flat notes, sometimes called correspondence cards, were for men and folded, sometimes called informals, were for women.  Either folded or flat, the cards can be personalized with your monogram, full name or even your nickname for casual correspondence.  Notes can be used to write thank you notes and also notes of sympathy, congratulations or when you’d just like to let someone know you’re thinking of them.