Atomic Swap
A trustless exchange of coins across two blockchains that either completes fully or not at all — no intermediary.
An atomic swap lets two parties trade coins on different blockchains directly, with a cryptographic guarantee that the trade either happens completely or not at all — neither party can take the other’s coins and run. It uses hash-time-locked contracts: both sides lock funds against a shared secret with a time limit, so revealing the secret to claim one side automatically enables claiming the other.
Atomic swaps embody the trustless ideal — cross-chain trading with no exchange or bridge custodian. In practice they’re limited by requiring compatible chains, online coordination, and liquidity, so they never displaced exchanges for everyday trading. But the concept underpins parts of the Lightning and cross-chain ecosystem, and demonstrates what “trustless” can mean concretely.