Using the definition from Merriam Webster, a postcard is “a card on which a message may be written for mailing without an envelope and to which the sender must affix a stamp”.
Simple, but effective definition.
It does distinguish between postcards from postal cards, which are postcards made by governments with pre-printed stamps on them.
I have disqualified other items from the Collection if they have an envelope or if they are not able to be mailed (then they are either just mail or souvenirs). This definition includes foldout postcards, where the postcards is one sheet of paper that is folded into multiple panels that collapse into one. I have one postcard where the postcard is an envelope (containing a DVD) but this may be cheating as then any pretty envelope could be considered a postcard.
I also disqualify promotional cards (even if they are mailed) unless there is room for the sender to ascribe a message and it has a postal address (i.e. not junk mail hand-delivered to everyone in a neighbourhood). Here’s a good example that mimics postcards but isn’t one!
I’m not official, however, sometimes people make postcards out of unconventional things or subvert promotional cards by squeezing in their own message. As long as there is
- customizable postal address (or space for one)
- a message (preferably personalized)
- a stamp (pre-printed, bulk-mailer inked, or paper) or space for a stamp
- is mailable without an envelope needed
Standard Postcard Sizes
- Small: 8.8 centimetres high by 14 cm. long (most common size until approx. 1970s)
- Medium / Average: 10.5 cm. x 15 cm. (probably most common size nowadays)
- Large: 11.7 cm. x 16.9 cm.
- Long: 10.1 cm. x 22.9 cm.