Delegated authentication
When a card issuer lets a wallet or merchant perform strong customer authentication on its behalf and accepts the result as its own.
PSD2 puts responsibility for strong customer authentication on the issuer, the customer's bank. But the bank isn't always closest to the customer. Someone paying with Apple Pay has already shown their face to the phone, and bouncing them to a banking app for a second check would be pointless and bad for conversion. The fix is contractual: the issuer outsources authentication to the wallet, which vouches that it was done.
Technically an attestation travels with the transaction. The issuer can still decline, but doesn't need to trigger its own 3-D Secure challenge. Legally the issuer remains answerable to the regulator, which is why such agreements have mostly gone to the big wallets and a handful of giant merchants.