All terms
A change to the rules, or a split into two chains.
A soft fork tightens rules so old nodes still accept new blocks. A hard fork changes them incompatibly, so everyone must upgrade or end up on a separate chain.
Contentious hard forks create two chains and two assets. Bitcoin Cash and Ethereum Classic both came from disagreements that could not be resolved.
Ethereum's move to proof of stake was a planned hard fork with near universal agreement, so no lasting split occurred.
Where to go next
More technology terms
Want this explained out loud?
Some of these land faster in conversation than in writing. Sessions are one to one and you can ask anything, including the things that feel too obvious to ask.