Glossary
Soft Fork
A backward-compatible blockchain protocol upgrade — tightens the rules so that all blocks valid under the new rules are also valid under the old rules.
A soft fork tightens a blockchain's rules. Blocks produced under the new rules remain valid under the old rules, so non-upgraded nodes still follow the chain — they just don't enforce the new restrictions. As long as a majority of mining or staking power upgrades, the soft fork takes effect without splitting the chain.
Bitcoin's SegWit (2017) and Taproot (2021) were soft forks; Ethereum's DAO fork was a hard fork. Soft forks are politically easier because they don't force every node to upgrade, but they can only add restrictions — never relax them.