Generally, a smart business card is any medium or object that has a chip within it for the purposes of storing and sharing contact information usually without physical contact.
The most popular ones are made of any of the following materials: metal, wood, and plastic; usually of rectangular shape, the size of a bank card, and run on near-field communication (NFC) technology (similar technology being used for modern contactless payment bank cards) without the absolute need for the installation of an app.
That said, a smart business card can be of any material or shape; the most important component is the presence of the NFC chip or similar technology integrated into it.