A replay attack occurs when a transaction that has been broadcast over a network is captured and reused by an attacker. This can happen in systems where two different networks or chains share the same address space and transaction format.For instance, if someone makes a transaction on one blockchain, an attacker could intercept that transaction and resend it on another blockchain, potentially causing the original sender to unintentionally spend their assets twice. These attacks exploit the similarities between chains, particularly in scenarios involving forks or multi-chain systems. To prevent replay attacks, developers often implement measures like transaction signatures that are chain-specific, ensuring that a transaction meant for one chain cannot be reused on another. Overall, understanding and mitigating the risks of replay attacks is crucial for maintaining the security and integrity of transactions in decentralized networks.