Base & Arbitrum Layer 2 Glossary

Fifteen terms you actually run into when using Base or Arbitrum, in plain English. Each definition stays short on purpose — if a word needs more than a couple of sentences, the linked guide has the numbers.

Layer 2 (L2)

A Layer 2 (L2) is a separate network that executes transactions off Ethereum mainnet and posts compressed proof of them back to Ethereum, inheriting mainnet security while charging a fraction of the fees. Base and Arbitrum are both Ethereum Layer 2 optimistic rollups.

See: What is Ethereum Layer 2 gas · Live L2 gas tracker

Gas fee

A gas fee is the payment for executing a transaction, calculated as gas units used multiplied by the gas price. On Base and Arbitrum a typical token swap costs about $0.002 to $0.01, compared with $2 to $30 on Ethereum mainnet.

See: Gas fee statistics · Base gas fee guide

Gwei

Gwei (gigawei) is the denomination gas prices are quoted in; one gwei equals 0.000000001 ETH. Layer 2 gas prices are often fractions such as 0.01 gwei because most of the total fee is charged separately as an L1 data fee.

See: What is gwei on Base and Arbitrum

Gas limit

The gas limit is the maximum number of gas units a transaction may consume. A simple ETH transfer always uses exactly 21,000 units; swaps, mints and contract calls use more, and wallets estimate the limit before you sign.

See: Base gas calculator

Optimistic rollup

An optimistic rollup is a Layer 2 that assumes transactions are valid by default and posts them to Ethereum in compressed batches; invalid batches can be challenged during a dispute window. This design lets Base and Arbitrum inherit Ethereum security without paying mainnet execution costs.

See: What is Ethereum Layer 2 gas

L1 data fee

The L1 data fee is the part of a Layer 2 transaction cost that pays for posting compressed transaction data to Ethereum mainnet. It follows mainnet congestion rather than activity on the L2, which is why Base and Arbitrum fees rise together whenever mainnet gwei spikes.

See: Arbitrum gas fees explained

EIP-4844 blob

EIP-4844 (proto-danksharding) introduced dedicated "blob" data space on Ethereum in March 2024 and cut the data cost rollups pay by roughly 90%. Cheap blobs are the main reason L2 transaction prices fell to sub-cent levels during 2024-2026.

See: Base vs Polygon gas fees

Sequencer

A sequencer is the operator that orders and instantly confirms transactions on a rollup before they settle to Ethereum. The Base and Arbitrum sequencers give soft confirmation in about 2 seconds and 0.25 seconds respectively; final settlement to Ethereum takes longer.

See: Base tracker · Arbitrum tracker

Finality

Finality is the point at which a transaction cannot be reversed. Base and Arbitrum provide near-instant soft confirmation, but official withdrawals to Ethereum mainnet take about 7 days because of the optimistic challenge period; fast third-party bridges settle withdrawals in minutes for a fee.

See: Bridge costs explained

RPC endpoint

An RPC endpoint is the server a wallet or app calls to read blockchain data and broadcast transactions. Default public endpoints include mainnet.base.org and arb1.arbitrum.io/rpc, with publicnode.com and Ankr commonly used as backups.

See: Add Base to MetaMask

Chain ID

A chain ID is a number that uniquely identifies an EVM network so wallets route transactions to the correct chain. Base mainnet is 8453 (Base Sepolia testnet 84532); Arbitrum One is 42161 and Arbitrum Nova is 42170.

See: Add Arbitrum to MetaMask

Bridge

A bridge moves assets between networks by locking tokens on the source chain and releasing or minting them on the destination. Official bridges take about 7 days and cost mainnet gas; fast bridges such as Across or Hop settle in minutes for roughly $0.10-0.40 on small transfers.

See: Why bridging to Arbitrum costs $5

ERC-20 approval

An ERC-20 approval is a separate transaction granting a smart contract permission to spend a token from your wallet. It costs its own gas fee the first time you trade a token, which is why a swap sometimes asks for two wallet confirmations.

See: ERC-20 approval fees explained

Wei

Wei is the smallest unit of Ether: one ETH equals 10 to the power 18 wei, and one gwei equals 10 to the power 9 wei. Wallets ultimately convert gwei and gas units into wei before showing the fee in ETH or dollars.

See: What is gwei

Smart contract

A smart contract is self-executing code deployed on-chain that powers tokens, swaps, mints and bridges. Interacting with one uses far more gas than a plain transfer because the network executes every instruction the contract contains.

See: Uniswap fees on L2