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Glossary of Arbitrum Terms

Active Validator

A staked Validator that makes disputable assertions to advance the state of an Arbitrum chain or to challenge the validity of others' assertions. (Not to be confused with the Sequencer ).

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 Ethereum and Arbitrum that facilitate trustless movement of ERC-20 tokens between L1 and L2.


A suite of Ethereum layer-2 scaling technologies built with the Arbitrum Nitro tech stack that includes Arbitrum One (a live implementation of the Arbitrum Rollup Protocol) and Arbitrum Nova (a live implementation of the Arbitrum AnyTrust Protocol).

Arbitrum AnyTrust Chain

An Arbitrum chain that implements the Arbitrum AnyTrust Protocol.

Arbitrum AnyTrust Protocol

An Arbitrum protocol that manages data availability with a permissioned set of parties known as the Data Availability Committee (DAC). This protocol reduces transaction fees by introducing an additional trust assumption for data availability in lieu of Ethereum's Trustless data availability mechanism. Arbitrum Nova is an example of an AnyTrust chain; Arbitrum One is an alternative chain that implements the purely trustless (and more L1-gas intensive) Arbitrum Rollup Protocol.

Arbitrum chain

A blockchain that runs on the Arbitrum protocol. Arbitrum chains are EVM compatible, and use an underlying L1 (Ethereum) for settlement and for succinct fraud-proofs (as needed). Arbitrum chains come in two forms: Arbitrum Rollup Chains and Arbitrum AnyTrust Chains.

Arbitrum Classic

Old Arbitrum stack that used custom virtual machine ("AVM"); no public Arbitrum chain uses the classic stack as of 8/31/2022 (they instead use Arbitrum Nitro ).

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 Nitro

Current Arbitrum tech stack; runs a fork of Geth directly on Layer 2 (L2) and uses WebAssembly as its underlying VM for fraud proofs.

Arbitrum Nova

The first Arbitrum AnyTrust Chain running on Ethereum mainnet. Introduces cheaper transactions; great for gaming and social use-cases. Implements the Arbitrum AnyTrust Protocol, not the Arbitrum Rollup Protocol protocol.

Arbitrum One

The first Arbitrum Rollup Chain running on Ethereum mainnet. Fully trustless; inherits Ethereum's base-layer security guarantees without introducing additional trust assumptions; great for decentralized finance and other use-cases that demand L1-level trustlessness.

Arbitrum Orbit

Arbitrum Orbit refers to the ability for anyone to permissionlessly deploy Layer 3 (L3) chains on top of Arbitrum Layer 2 (L2) chains.

Arbitrum Rollup Chain

An Arbitrum chain that implements the Arbitrum Rollup Protocol.

Arbitrum Rollup Protocol

A trustless, permissionless Arbitrum Layer 2 (L2) protocol that uses its underlying base layer (i.e., Ethereum) for data availability and inherits its security. This protocol is implemented by our Arbitrum One chain.


Layer 2 "operating system" that trustlessly handles system-level operations; includes the ability to emulate the EVM.


A staked claim by an Arbitrum Validator. An assertion may, e.g., propose a new RBlock, or may be a step in a Challenge.


A group of L2 transactions posted in a single L1 transaction into the Fast Inbox by the Sequencer.


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.

🧢 CAP Finance

Widely considered the most degen community on Arbitrum.

CAP is a decentralized trading protocol. It's designed to be fast and easy to use by anyone.

Chain state

A particular point in the history of an Arbitrum chain. A chain's state is determined by applying Arbitrum state-transition function to sequence of transactions (i.e., the chain's history).


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 L1. 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 (1 week on Arbitrum One) over which an asserted RBlock can be challenged, and after which the RBlock can be confirmed.

Challenge protocol

The protocol by which RBlocks are submitted, disputed, and ultimately confirmed. The Challenge Protocol guarantees that only valid RBlocks will be confirmed provided that there is at least one honest Active Validator.


A program running on a user's machine, often in the user's browser, that interacts with contracts on an Arbitrum chain and provides a user interface.


The decision by an Arbitrum chain to finalize an RBlock as part of the chain's history. Once an RBlock is confirmed its L2 to L1 Messages (e.g., withdrawals) can be executed.

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.


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

Data Availability Certificate

Signed promise from a Data Availability Committee (DAC) attesting to the availability of a batch of data for an Arbitrum AnyTrust Chain.

Data Availability Committee (DAC)

A permissioned set of parties responsible for enforcing data availability in an Arbitrum AnyTrust Protocol chain. See Introducing AnyTrust Chains: Cheaper, Faster L2 Chains with Minimal Trust Assumptions to learn more.

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

A contract that holds L1 initiated messages to be eventually included in the Fast Inbox. Inclusion of messages doesn't depend on the Sequencer.


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

💎 Dopex

A shiny gem in the Arbitrum community.

Commonly associated with the esteemed Diamond Pepe's NFT and Dopex community. Dopex is a decentralized options exchange protocol on Arbitrum.

Ethereum Wallet

A software application used for transacting with the Ethereum Blockchain.

Fair Ordering Algorithm

BFT algorithm in which a committee comes to consensus on transaction ordering; current single-party Sequencer on Arbitrum may eventually be replaced by a fair-ordering committee.

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

Contract that holds a sequence of messages sent by clients to an Arbitrum Chain; a message can be put into the fast Inbox directly by the Sequencer or indirectly through the Delayed Inbox.


Censorship resistant path for including a message into L2 via the Delayed Inbox; bypasses any Sequencer involvement.

Fraud proof

The means by which an Active Validator proves to its underlying chain that an invalid state transition has taken place.

Gas Price Floor

Protocol-enforced minimum gas price on an Arbitrum chain; currently 0.1 gwei on Arbitrum One and 0.01 gwei on Arbitrum Nova.

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.


An execution-layer client that defines the Ethereum state transition function and handles network-layer logic like transaction memory pooling. Arbitrum Nitro utilizes a fork of Geth to implement Arbitrum's state transition function.


If you've seen some blueberries wandering around on crypto Twitter, you might wonder .. where did they come from?

The iconic blueberries come from the community of the decentralized exchange, GMX.

L2 Block

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

L2 to L1 Message

A message initiated from within an Arbitrum chain to be eventually executed on Layer 1 (L1) (e.g., token or Ether withdrawals). On Rollup chains like Arbitrum One, the Challenge Period must pass before an L2 to L1 message is executed.

Layer 1 (L1)

The base protocol and underlying blockchain of the Ethereum network. Responsible for maintaining the integrity of the distributed ledger and executing smart contracts. Contains both Ethereum's execution layer and consensus layer.

Layer 2 (L2)

Trustless scaling solutions built on top of Ethereum's Layer 1 (L1) base protocol, such as state channels, plasma chains, optimistic rollups, and ZK-rollups. Layer 2 solutions aim to increase scalability and reduce the cost of transactions on Ethereum's Layer 1 without introducing additional trust assumptions.

Layer 3 (L3)

An Arbitrum chain whose core contract reside on an Arbitrum Layer 2 (L2) chain.

One Step Proof

Final step in a challenge; a single operation of the L2 VM (Wasm) is executed on L1, and the validity of its state transition is verified.


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.

🏴‍☠️ Pirate Nation

If you sail in the deep blue seas of Arbitrum, you may encounter some ships with pirate flags along the way ARRGG!

The pirate flag originates from the Pirate Nation community. Pirate Nation is a game filled with high seas adventure, treasure, fun, and unexpected surprises.


An assertion by an Arbitrum Validator that represents a claim about an Arbitrum chain's state.

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

A Token Gateway in which the L2 Gateway contract escrows and releases tokens, which the L1 Gateway contract mints and burns tokens. This in the inverse to how "typical" gateways work.


An entity (currently a single-party on Arbitrum One) given rights to reorder transactions in the Fast Inbox over a fixed window of time, who can thus give clients sub-blocktime Soft Confirmations. (Not to be confused with a Validator).

Sequencer Feed

Off chain data feed published by the Sequencer which clients can subscribe to for Soft Confirmations of transactions before they are posted in Batches.

Smart Contract

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

🐵 Smolverse

Near the core of Arbitrum community is Smolverse, a world filled with Smol Brains and Smol Bodies.

If you see any Smol's with giga brains, swole arms or hear the sound of "EEEE" in the Arbitrum community, you've encounted the Smol Brains and Smol Bodies.

Soft Confirmation

A semi-trusted promise from the Sequencer to post a user's transaction in the near future; soft-confirmations happen prior to posting on L1, and thus can be given near-instantaneously (i.e., faster than L1 block times)

Speed Limit

Target L2 computation limit for an Arbitrum chain. Arbitrum One and Arbitrum Nova currently target 7,000,000 gas / second. When computation exceeds this limit, fees rise, ala EIP-1559.


A Validator who deposits a stake (in Ether on Arbitrum One and Arbitrum Nova ) to vouch for a particular RBlock in an Arbitrum Chain. A validator who stakes on a false RBlock can expect to lose their stake. An honest staker can recover their stake once the RBlock they are staked on has been confirmed.

Standard Arb-Token

An L2 token contract deployed via the StandardERC20 gateway; offers basic ERC20 functionality in addition to deposit / withdrawal affordances.

StandardERC20 gateway

Token Gateway via which any L1 ERC20 token can permissionlessly bridge; the StandrardERC20 gateway contracts deploy a Standard Arb-Token on L2 for each bridged token.


Upcoming upgrade to the the Arbitrum Nitro virtual machine that will allow smart contract support for languages like Rust and C++ by taking advantage of Nitro's use of WASM (read more).

🏹 Tales of Elleria

The bow and arrow are commonly associated with the Hero's of Tales of Elleria.

Jump into the world of Elleria and go on adventures.

🐸 Toadstoolz

Hidden in the Croakshire, you will find the friendly Toadstoolz.

The iconic Toads of Arbitrum love to hunt BUGZ
and collect NFTs. !CROAK

Token Gateway

A pair of contracts in the token bridge — one on L1, one on L2 — that provide a particular mechanism for handling the transfer of tokens between layers. Token gateways currently active in the bridge include the StandardERC20 gateway , the Generic-Custom Gateway , and the WETH Gateway.

🏡 TownStory

If you see some homes along your road trip in the Arbitrum ecosystem, you've made it to TownStory.

Build a warm and prosperous town with friends in TownStory.


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

✨ Treasure DAO

While exploring the Arbitrum ecosystem, you may see some shining stars.

The iconic stars symbolize the magic of Treasure DAO. Treasure DAO is the decentralized gaming ecosystem connecting games and players on Arbitrum.


In the context of Ethereum, trustless refers to the ability of a system to operate without reliance on a central authority or intermediary. Instead, users place their trust in math and protocols.

This is achieved through the use of cryptographic techniques and decentralized consensus mechanisms that let users verify the integrity of network transactions using open-source software. Trustless systems are considered to be more secure and resistant to fraud or tampering because they don't rely on a single point of failure that can be exploited by attackers.


An Arbitrum Full Node that tracks the status of the chains' Assertions. A validator may be a Watchtower Validator, a Defensive Validator, or an Active Validator.

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 upwraped on L1 and rewrapped on L1 upon depositing (and vice-versa upon withdrawing), ensuring WETH on L2 always remains collatoralized.

👺 Zeeverse

As you're exploring the Arbitrum world, you may bump into a world filled with monsters and Zee's.

Explore a mythical Spirit Realm as a young Shaman and take part in strategic turn-based battles to help protect Zeeverse from the looming corrupted forces.