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Arbitrum glossary

Address Alias

An address deterministically generated from an L1 contract address used on L2 to safely identify the source of an L1 to L2 message.

Arb Token Bridge

A series of contracts on an Arbitrum chain and its underlying chain that facilitate trustless movement of ERC-20 tokens between the two layers.

Arbified Token List

A token list that conforms to Uniswap's token list specification; Arbified lists are generated by inputting externally maintained list (

i.e., coinmarketcap's list

) and outputting a list that includes all of the instances of token contracts on the Arbitrum chain bridged via the canonical Arb Token Bridge from tokens on the inputted list. (See code here .)

Arbitrum

Arbitrum Bridge UI

Web application built and maintained by Offchain Labs for user-interactions with the Arb Token Bridge; visit it here.

Arbitrum Classic

Arbitrum Full Node

A party who keeps track of the state of an Arbitrum chain and receives remote procedure calls (RPCs) from clients. Analogous to a non-staking L1 Ethereum node.

Arbitrum Orbit

Layer 3 (L3)

ArbOS

Arbitrum's "operating system" that trustlessly handles system-level operations; includes the ability to emulate the EVM.

Assertion

A staked claim made by an Arbitrum Validator representing a claim about an Arbitrum chain's state. An Assertion may, e.g., propose a new assertion, or may be a step in a Challenge.

Auction Contract

A smart contract that handles the state, accounting of funds for bids, and various operations of the Timeboost auction. The contract is deployed on the target chain for which Timeboost is enabled.

Autonomous Auctioneer

Off chain software that receives bids from Timeboost participants, processes and validates bids, and then posts the top valid bid (or top two valid bids in the case of a tie) to the Auction Contract to resolve the on-going Timeboost auction. The autonomous auctioneer, for a given chain, is provisioned & deployed by an entity designated by the chain's owner.

Batch

Underlying Chain, Fast Inbox

Blockchain

A distributed digital ledger that is used to record transactions and store data in a secure, transparent, and tamper-resistant way, notably in cryptocurrency protocols.

BLS Signature

BoLD

Short for "Bounded Liquidity Delay"; latest version of the Arbitrum Challenge protocol designed to eliminate

delay attack vectors

(see

here

for more). Not currently on mainnet.

Bridge

Cross-chain message

Chain Owner

An entity (i.e., a smart contract) with affordance to carry out critical upgrades to an Arbitrum chain's core protocol; this includes upgrading protocol contracts, setting core system parameters, and adding and removing other chain owners.

Chain state

Challenge

When two Stakers disagree about the correct verdict on an Assertion, those stakers can be put in a challenge. The challenge is refereed by the contracts on the underlying chain. Eventually one staker wins the challenge. The protocol guarantees that an honest party will always win a challenge; the loser forfeits their stake.

Challenge Period

Window of time (one week on Arbitrum One) over which an Assertion can be challenged, and after which the assertion can be confirmed.

Challenge protocol

Assertion

Client

Confirmation

Assertion, L2 to L1 Message

Cross-chain message

An action taken on some chain A which asynchronously initiates an additional action on chain B.

Custom Arb-Token

Any L2 token contract registered to the Arb Token Bridge that isn't a standard arb-token (i.e., a token that uses any gateway other than the StandardERC20 gateway ).

Custom gateway

Any Token Gateway that isn't the StandardERC20 gateway.

dApp

Short for "decentralized application." A dApp typically consists of smart contracts as well as a user-interface for interacting with them.

Data Availability Certificate

Defensive Validator

A Validator that watches an Arbitrum chain and takes action (i.e., stakes and challenges) only when and if an invalid Assertion occurs.

Delayed Inbox

Fast Inbox

Dev-Tools Dashboard

Web application built and maintained by Offchain Labs for developers and users to debug Arbitrum transactions; i.e., executing or checking the status of Cross-chain messages; visit it here.

Dissection

A step in the Challenge protocol in which two challenging parties interactively narrow down their disagreement until they reach a One Step Proof.

Ethereum Wallet

A software application used for transacting with the Ethereum Blockchain.

EVM+

The paradigm introduced by Stylus in which Arbitrum's EVM compatibility is preserved while new features and improvements are introduced.

Express Lane

Timeboost

Express Lane Controller

An address, defined in the Auction Contract, that is granted the privilege to use the Express Lane. These privileges are granted after verifying that the incoming transactions were properly signed by the express lane controller, among other checks.

Fair Ordering Algorithm

Fast Exit / Liquidity Exit

A means by which a user can bypass an Arbitrum chain's Challenge Period when withdrawing fungible assets (or more generally, executing some "fungible" L2 to L1 operation); for trustless fast exits, a liquidity provider facilitates an atomic swap of the asset on L2 directly to L1.

Fast Inbox

Delayed Inbox

First Come First Serve (FCFS)

A type of Transaction Ordering Policy used by the sequencer in Arbitrum chains whereby incoming transactions are sequenced into a block in the order that the transactions arrived.

Force-Inclusion

Delayed Inbox

Fraud proof

Gas Price Floor

Gateway Router

Contracts in the Arb Token Bridge responsible for mapping tokens to their appropriate Token Gateway.

Generic-Custom Gateway

A particular Custom gateway via which an L1 token contract can be registered to a token contract deployed to L2. A useful alternative to the StandardERC20 gateway for projects that wish to control the address of their L2 token contract, maintain L2 token contract upgradability, and for various other use-cases.

Ink

The equivalent of gas in the Stylus vm. Ink is introduced for finer granularity than gas offers since Stylus's operations are considerably cheaper than their EVM analogs.

L2 Block

Data structure that represents a group of L2 transactions (analogous to L1 blocks).

L2 to L1 Message

Challenge Period

Layer 3 (L3)

Native Fee Token

Arbitrum Orbit

Offchain Labs

One Step Proof

Final step in a challenge; a single operation of the Arbitrum VM ( WASM ) is executed on the underlying chain, and the validity of its state transition is verified.

Outbox

An L1 contract responsible for tracking L2 to L1 Messages, including withdrawals, which can be executed once they are confirmed. The outbox stores a Merkle Root of all outgoing messages.

Portal

A web application maintained by Offchain Labs showcasing the Arbitrum ecosystem; visit it here.

RBlock

Refer to Assertion

Reorg

A situation in which transactions on a chain that were at some point considered accepted then get rejected. In the context of an Arbitrum chain, once transactions are posted in the chain's Fast Inbox, the only way the chain can experience a reorg is if its Underlying Chain itself reorgs. Of note, Fraud proofs do not cause reorgs.

Retryable Autoredeem

The "automatic" (i.e., requiring no additional user action) execution of a Retryable Ticket on an Arbitrum chain.

Retryable Redeem

The execution of a Retryable Ticket on L2; can be automatic (see Retryable Autoredeem) or manual via a user-initiated L2 transaction.

Retryable Ticket

An L1 to L2 cross chain message initiated by an L1 transaction sent to an Arbitrum chain for execution (e.g., a token deposit).

Reverse Token Gateway

Token Gateway

Sequencer Feed

Soft Confirmation, Batch

Shared Sequencing

Smart Contract

A computer program whose operations are defined and executed within a blockchain consensus protocol.

Soft Confirmation

Speed Limit

Staker

Validator, Assertion

Standard Arb-Token

An token contract on an Arbitrum chain deployed via the StandardERC20 gateway; offers basic ERC20 functionality in addition to deposit / withdrawal affordances.

StandardERC20 gateway

Token Gateway, Standard Arb-Token

State Transition Function

The STF (State Transition Function) defines how new blocks are produced from input messages (i.e. transactions) in an Arbitrum chain.

Stylus

Timeboost

Token Gateway

StandardERC20 gateway, Generic-Custom Gateway, WETH Gateway

Transaction

A user-initiated interaction with a Blockchain. Transactions are typically signed by users via wallets and are paid for via transaction fees.

Transaction Ordering Policy

The rules and logic employed by a chain to order incoming transactions into a block.

Underlying Chain

Validator

Arbitrum Full Node, Assertion, Watchtower Validator, Defensive Validator

WASM

Fraud proof,Stylus

WASMer

A popular WebAssembly runtime for executing WASM binaries. A fork of WASMer is used for executing Stylus programs. WASMer executes considerably faster than Geth executes EVM code, contributing to Stylus's lower fees.

Watchtower Validator

A Validator that never stakes / never takes on chain action, who raises the alarm (by whatever off-chain means it chooses) if it witnesses an invalid assertion.

WETH Gateway

Token Gateway for handing the bridging of wrapped Ether (WETH). WETH is unwrapped on L1 and rewrapped on L1 upon depositing (and vice-versa upon withdrawing), ensuring WETH on L2 always remains collateralized.