Application security is the practice of finding and reducing risks in software applications and the components they rely on, such as libraries, APIs, runtimes, and configuration. It covers secure design, code review, dependency management, vulnerability testing, patching, and hardening. The goal is to prevent defects from becoming exploitable weaknesses in production.
It matters because attackers often target the application layer: injection flaws, broken authentication, insecure deserialization, exposed secrets, and vulnerable third-party components can all lead to data theft, service disruption, or deeper compromise. Defenders use application security tools and processes to catch these issues before deployment and to track them after release. In modern systems, including AI-enabled applications, it also means linking assets to weakness data so teams can prioritize what to fix first instead of relying on a static inventory alone.