Trustless is the adjective behind the entry on trustless systems, which explains how blockchains and related technologies remove the need for trusted intermediaries. This page explains the single word, which is common in crypto marketing and technical writing.
In crypto, calling something trustless means that users do not have to rely on the honesty of a particular person, company or institution for it to work as promised. Instead, outcomes are enforced by open rules: transactions are checked by many independent computers under a consensus mechanism, ownership is proven with cryptographic keys, and agreements are carried out by smart contracts. A trustless exchange, for example, lets two people swap tokens without either sending funds first or handing them to a custodian, a contrast captured in the debate over custodial versus non-custodial services.
The word is often misunderstood. It does not mean the system is untrustworthy; it means trust is moved from people to software, mathematics and economic incentives. Many specialists prefer the phrase "trust-minimized", because users still trust the code to be free of bugs, the network to stay decentralized and the hardware and wallets they use. Exchange collapses and smart contract hacks have shown that services described as trustless can still fail. The idea links to the slogan "not your keys, not your coins" and to broader study of trust in economics.