Soft Fork

A soft fork is a backward-compatible update to a blockchain's protocol. Unlike a hard fork, a soft fork does not require all nodes to upgrade in order to continue participating in the network. Nodes running the old software can still recognize new blocks as valid, though they may not be able to use the new features. Soft forks typically require majority miner or validator agreement and do not result in a permanent chain split. An example is Bitcoin's SegWit upgrade.