`std::invalid_argument` is a standard exception class in C++ that is part of the std namespace. It is used to indicate that a function has received an argument that is not valid or appropriate for its operation. This exception helps developers identify and handle errors related to incorrect input, improving the robustness of their code. When a function throws a `std::invalid_argument` exception, it typically provides a message that describes the issue. This allows programmers to understand what went wrong and take corrective action. Using this exception promotes better error handling and enhances the overall reliability of C++ applications.