Proof of work buys agreement with energy, proof of stake with capital at risk. Other families exist, including the federated agreement used by Stellar and the validator-list model used by the XRP Ledger.
It is the foundational design choice of any chain, determining who can add blocks, what attacking costs, and whether the coin can be mined at all.
This definition is educational and not financial advice. Crypto is volatile and high-risk — always do your own research.
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