Google Smart Tap is the protocol an Android phone uses to transmit a Google Wallet pass over NFC. When a member holds their phone to a capable reader, the wallet selects the right pass and sends its payload, typically a member identifier, encrypted for that merchant, without the member opening anything.
Smart Tap is permissioned on both ends. The pass must be created with Smart Tap enabled and reference the merchant's Smart Tap identifiers, and the reader must hold the matching keys. This is set up between the wallet platform, the merchant and the reader or terminal provider, and once configured it applies to every pass in the program.
At the till, Smart Tap and Apple VAS are two halves of the same experience: one reader configuration, one tap target, and members on either platform identified the same way. On payment terminals that support it, the identification rides along with the payment tap itself.
Two practical notes. First, Smart Tap support varies by reader and terminal vendor, so certification on the merchant's actual hardware is the thing to verify, not the protocol name on a datasheet. Second, NFC is one of two equal routes: a Google Wallet pass can also carry a QR code or barcode, which works on any scanner the merchant already owns. A program should treat both as first-class and let the hardware decide.