Sticker cards are exactly what they sound like — cards with a peel-off sticker backing. Peel the back off and you've got a sticker you can stick wherever you want (though most collectors keep them intact).
The most famous sticker cards in the hobby? Garbage Pail Kids and Wacky Packages — two legendary Topps brands built entirely around the sticker card format. Both became cultural phenomena and remain hugely collectible today.
Sticker cards add a playful, interactive element to collecting that traditional cards don't offer. They're a reminder that the hobby has always had a fun, irreverent side alongside the serious collecting.