Validation is the process of testing a build, binary, firmware image, or configuration to confirm that its measured behavior matches what was expected. In security work, that means checking more than whether something compiles or installs: you measure runtime behavior, resource use, network activity, outputs, and error handling against a known-good baseline.
Validation matters because small changes can create big security gaps. A rebuilt tool may carry a new dependency, a different compiler flag, or an altered power stage that changes how it behaves in the field. Defenders use validation to catch tampering, supply-chain drift, and unsafe configuration changes before release. Attackers also rely on the absence of validation, exploiting software or devices that were never tested on the exact parts, inputs, or environments they use in practice. Good validation makes reuse safer by proving that the real build still behaves like the design.