A "Gray Box" is a term used in various fields, including software testing and security. It refers to a testing approach that combines both black box and white box testing methods. In gray box testing, the tester has partial knowledge of the internal workings of the system, allowing them to design test cases that are more effective than those based solely on external behavior. This method is particularly useful in identifying vulnerabilities in software applications. By understanding some of the internal structures while also observing how the system behaves from the outside, testers can uncover issues that might not be visible through either black box or white box testing alone.