Arbitrum One is a specific instance of Arbitrum, which is the first mainnet deployment of Arbitrum. It is a layer 2 scaling solution for the Ethereum network, developed by Offchain Labs.
Arbitrum One uses Optimistic Rollups technology to bundle multiple transactions together and batch them into a single transaction on the Ethereum network, which helps to reduce congestion and increase transaction throughput. It is designed to be compatible with the existing Ethereum ecosystem, including smart contracts, dApps, and other Ethereum-based applications.
Arbitrum One has gained popularity in the Ethereum community due to its fast and cheap transaction processing, which allows users to avoid the high fees and slow confirmation times that are often associated with the Ethereum mainnet. It is also known for its ease of use and developer-friendly features, such as the ability to deploy smart contracts on the Arbitrum One network using familiar tools like Remix and Truffle.