> For the complete documentation index, see [llms.txt](https://docs.space.id/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.space.id/payment-id/key-terms.md).

# Key Terms

* **Payment ID:** A human-readable identifier (like alice\@binance) that maps to multiple blockchain addresses across different sources and networks.
* **ZK Email:** A privacy-preserving technology that uses zero-knowledge proofs to verify email ownership and content without revealing the actual email address on-chain, serving as the identity layer for Payment ID.
* **Wallet:** A deterministic smart contract wallet derived from a user's email address using zero-knowledge proofs. Each email maps to exactly one wallet, providing a consistent on-chain identity while keeping the email private and enabling transaction execution through ephemeral session keys.
* **PID Token:** An ERC-721 non-fungible token that represents ownership of a Payment ID, allowing for transfers and delegated management.
* **Resolver:** A smart contract that maps Payment IDs to blockchain addresses based on the source context (exchange/wallet/anything) and blockchain network.
* **Source Type:** An identifier for different sources of funds (exchanges, wallets, anything) that allows a single Payment ID to have different addresses for different contexts (e.g., @binance, @metamask, @mytopaccount).


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