QSL cards have been long associated with HF but you’ll find them popular among satellite users and other groups where you want to confirm contacts. Jim takes a look at the key things you’ll find on a QSL card.
For more info on QSL Cards try this Wikipedia article: https://en.wikipedia.org/wiki/QSL_card
I have been happy with cards from https://www.kb3ifhqslcards.com/