What is a Bitcoin hard fork?

Related questions

1. What makes ethereum different?
2. What is a Chinese Dao?
3. Are ether and ethereum the same?
4. What is ether money?
5. What is a DAO software?
6. What happens hard fork?
7. Where can you buy ethereum Classic?
8. What does it mean when a Cryptocurrency Forks?
9. Which country currency is ether?
10. Is ethereum a currency?

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22. #sometimes