Arbitrum is a layer 2 scaling solution for Ethereum, designed to increase the network's transaction throughput and reduce gas fees. It uses a technology called Optimistic Rollups, which allows multiple transactions to be processed off-chain and then committed to the Ethereum blockchain in a single batch. This makes transactions faster and cheaper while still maintaining the security and decentralisation of the Ethereum network.
ARB is the native token of the Arbitrum network. It is used as a means of payment for transaction fees on the network and as a tool for governance, allowing holders to vote on important decisions related to the network's operation and development. Additionally, ARB can be staked to earn rewards, incentivising users to contribute to the network's security and decentralisation.