Smart contract audits are critical in the DeFi ecosystem to ensure the security and reliability of decentralized applications (dApps) by identifying vulnerabilities and coding inefficiencies before deployment on immutable blockchains. The audit process involves several steps, including documentation collection, automated and manual code reviews, error classification, and the generation of initial and final reports to address and resolve any issues found. Common vulnerabilities include reentrancy attacks, integer overflows, and function visibility errors, while gas optimization is important for efficient execution. Popular tools like Mythril and Slither assist in the auditing process, and audits typically cost between $5,000 and $15,000, depending on complexity. The process not only protects user funds from being irretrievably lost due to hacks but also enhances the overall robustness of protocols, thus contributing to the security and performance of Web3 applications.