What it physically is
Ten folded cards, A5, on a 350 gsm coated stock. Only one artwork file goes to the printer, which is why there's nothing on the inside at all and the whole of it is yours to write in.
Ten is not a bulk discount, it is the pack. That turns out to be the useful bit: it means there are spares in a drawer for the next occasion rather than one card for one birthday.
Who buys ten of something
Clubs and societies, mostly. A raffle prize at an open day, a thank-you for a visiting exhibitor, something to hand across with a layout, a card that goes round a group to sign. Families with more than one enthusiast in them come a close second.
Which photographs suit it
Almost anything, which is the point. A card is looked at from arm's length, so a file that is too soft for a wall print is usually fine here, and a tight detail shot that would be odd at A2 works well small. The card guide goes further into choosing one, and preparing the photograph covers the mechanics.
The alternatives
If the card is going with something bigger, the framed print is the usual pairing and can carry the same picture. The stage page holds every format we make.