A smart contract audit is a code review conducted by a specialist firm to identify vulnerabilities before or after a contract is deployed on-chain. Audits typically take 2-8 weeks and produce a public report listing findings by severity (critical, high, medium, low, informational), along with the team's response and any remediations.
Not all audits are equal. A 3-day automated scan from a low-tier firm is not comparable to a 6-week manual review from a top-tier firm with formal verification. Audit scope also matters: an audit of one contract doesn't cover others in the protocol, and an audit of v1 doesn't cover v2.