A JIT (Just-In-Time) compiler is a component of runtime environments that translates code into machine instructions as a program executes, rather than before execution. This allows for optimizations based on the actual usage patterns of the code. In cybersecurity, JIT compilers can be a target for attackers, as vulnerabilities may allow malicious code injection during the compilation process. Attackers exploit these weaknesses to insert hooks or alter program behavior at runtime, potentially bypassing security controls or executing unauthorized actions.