A dynamic QR code is a QR code whose destination sits behind a short redirect link you control, rather than being encoded in the printed pattern. A static QR code stores the full URL in its dots, so once it is printed it cannot change: a typo, a moved page, or an ended campaign means reprinting. A dynamic code stores only a short QR Cake link that forwards each scan to the destination you set. Because that link is short, the pattern also stays simple and scans well at small print sizes.
Free matters because a printed code should keep working without a subscription behind it. QR Cake's free plan is not a trial: you get up to 5 dynamic QR codes with unlimited scans, no credit card, and no expiration date, so a sticker on a package or a sign in a window keeps working for as long as your account exists. You can change each destination as often as you need. The trade-off is that scanners first see a short QR Cake page with a brief ad before your destination.
The redirect also makes scan analytics possible, and QR Cake includes them on the Pro and Business plans. There you can see total scans, scans by hour or day, the country and device type behind them, and compare two codes side by side, such as the flyer against the table tent. On the free plan the code redirects the same way, but analytics are not included.