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.
That a fork means a chain split. Most forks are coordinated upgrades that everybody adopts and nothing splits. A split only happens when part of the network refuses the new rules, which is rare and usually contentious.
Common questions
What is the difference between a hard and a soft fork?
Do I get free coins in a fork?
Where to go next
More technology terms
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