What Is the Concept of a “Soft Fork” versus a “Hard Fork” in Blockchain Upgrades?

A soft fork is a backward-compatible blockchain upgrade, meaning that non-upgraded nodes will still recognize the new blocks as valid, though they cannot enforce the new rules. A hard fork is a non-backward-compatible upgrade that requires all nodes to update; it results in a permanent split of the blockchain into two separate chains, where the old chain's blocks are considered invalid by the new chain's rules.

Soft forks are generally less disruptive than hard forks.