Can I understand what is meant by stock card?

71108530 : here

PaperTradingOfficial : Hi Mooer, When you have enough stock cards of the same type, you can use them to redeem real stocks to your securities account in the moomoo App（The validity period of stock cards is 365 days）If you dont have enough stock cards, you may wait and collect, until you have enough stock cards to redeem. (If you have not opened the securities account, please open the securities account within the validity period and redeem the corresponding stocks manually)