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Version: Endpoint V1


This glossary defines and explains many LayerZero concepts and terminology.

User Application (UA)

A User Application (UA) is any contract that uses LayerZero to send & receive messages between blockchains. We define UA as a tuple (chainId, contractAddress)

  • the UA that send() the message at the source chain as srcUA (srcChain, srcAddress)

  • the UA that lzReceive() at the destination chain as dstUA (dstChain, dstAddress)

In LayerZero's perspective, srcUA and dstUA are different, though they might be the same entity.

Ultra-Light Node (ULN)

ULN is a messaging protocol, firstly introduced in the LayerZero white paper, that allows lightweight cross-chain messaging with configurable trustlessness on the specification of Oracle and Relayer, the two roles that are relaying block information and transaction proof across chains.


A contract address that can be notified to move a block header.

What is a Relayer?

Any process that delivers a transaction proof in the LayerZero system.

Messaging Library

The contract that handles the message payload packing on the source chain and verification on the destination chain. Ultra-Light Node is an implementation of Messaging Library

Proof Library

The contract that verifies the validity of a proof. Merkle Patricia Tree inclusion proof is an implementation of Proof Library.