On-chain transactions and off-chain transactions differ in where they are recorded and settled. On-chain transactions occur directly on the blockchain, meaning that all transaction details are recorded and verified on the blockchain network. Off-chain transactions, on the other hand, are transactions that occur outside of the main blockchain network, often using secondary payment channels or networks. Off-chain transactions are typically faster and can have lower fees compared to on-chain transactions, but they may not offer the same level of security and decentralization.