In relation to blockchain technology, a soft fork involves introducing changes to a blockchain's underlining protocol or software that are minor in nature. These software updates can take the form of new blockchain functionality, upgrades to network performance, enhancements that correct security issues, or even changes to the consensus rules that govern how blocks are created and validated on a blockchain. Forks are necessary for providing decentralized blockchains a way to make changes to the blockchain since there isn't a central authority governing all aspects of blockchain development and evolution
Example
“Bitcoin's Segregated Witness (SegWit) upgrade was implemented as a soft fork, meaning older nodes could still validate transactions without upgrading, while updated nodes gained access to improved transaction throughput.”