Define ‘Double-Spending’ in the Context of Cryptocurrency

Double-spending is a flaw in a digital cash system where a single unit of currency is spent more than once. In traditional digital systems, this is prevented by a central authority.

In decentralized cryptocurrencies, consensus mechanisms like Proof-of-Work and Proof-of-Stake prevent it by ensuring transactions are grouped into blocks that are chronologically and cryptographically linked. Once a transaction is confirmed in the canonical chain, it is extremely difficult to reverse and spend the same coins again.