The changes implemented on a blockchain network to modify or add new features without causing any fundamental changes to the structure of the network are known as a soft fork. It ends the further validity of previous transactions that decide to follow the new rules of the consensus mechanism. However, the nodes that do not decide to follow the new rules can still operate following the old rules of the consensus. A soft fork, unlike a hard fork, is backward compatible.
The soft fork does not require all its miners to agree to the proposed change. It is implemented once the majority of the miners agree on it, leading to faster network upgrades without causing a commotion in the community. A soft fork can only be reversed with the help of a hard fork. Both Bitcoin and Ethereum have undergone several soft forks to upgrade their networks, fixing functionalities and adding new features.