On-chain

The term on-chain refers to transactions taking place directly on a blockchain, not through an intermediary such as a CEX. On-chain transactions are immutable and will be visible on the blockchain's public ledger. Transacting on-chain usually requires the user to have the blockchain's native gas currency. Typically, transactions on-chain can only be reversed if the majority of network participates agree to reverse or roll-back the transaction; this is referred to as a hard fork and it happened with Ether after the DAO hack.