`std::system_error` is a class in the C++ Standard Library that represents errors related to system calls and library functions. It is part of the `<system_error>` header and provides a way to handle errors that occur due to system-level issues, such as file access problems or resource allocation failures. This class encapsulates an error code and a corresponding error message, making it easier to diagnose issues in programs. When using `std::system_error`, developers can throw or catch exceptions that provide detailed information about the error. The class includes methods to retrieve the error code and message, allowing for better error handling and debugging. This is particularly useful in applications that rely on system resources, as it helps maintain robustness and clarity in error reporting.