Executable code is any program text or binary that a computer can run, including scripts, compiled applications, bytecode, and machine-generated output. In security work, the key idea is not who wrote it, but that the system will interpret it as instructions and act on them.
This matters because executable code can read files, start processes, connect to networks, or change system state. Attackers try to smuggle malicious logic into code reviews, package builds, or AI-assisted development workflows, where output may look correct but still contain unsafe behavior. Defenders treat executable code as something to verify, not trust: they use code review, sandboxing, static and dynamic analysis, signing, and least privilege to limit what code can do if it is flawed or hostile.