A dark-web marketplace is an online trading space, usually reachable through privacy-focused networks and not indexed by normal search engines, where criminals buy and sell stolen data, credentials, malware, counterfeit documents, and other illegal goods or services.
In cyber security, these marketplaces matter because they turn breaches into repeatable profit. Stolen records can be packaged, priced, and resold, making one intrusion useful for many attacks. Buyers may combine a name, SSN, email, or password into a fuller identity profile for fraud, account takeover, or business email compromise. Defenders watch these markets to understand what data is circulating, whether exposed credentials or executive identifiers are being traded, and how urgently accounts or verification processes need to be hardened. The key risk is not just theft, but the reuse and monetization of compromised information.