Correspondence cards are flat stationery cards (as opposed to fold-over) and usually far more simple in design with a name at the top center and maybe a motif in the corner. It’s a great card for a quick note and my personal favorite type of stationery.
My cards are standard A2 size (5 1/2″ x 4 1/4″ or 14 cm by 11 cm) and come with your choice of colored or white envelopes. I make it a point to use stock & envelopes that contain amounts of recycled material. I’m all about sending letters and using paper as long as it’s responsibly!