C++03 is a version of the C++ programming language standardized by the International Organization for Standardization (ISO) in 2003. It is an incremental update to the previous standard, C++98, and primarily focuses on bug fixes and clarifications rather than introducing new features. This version aimed to improve the language's consistency and usability for developers. Key improvements in C++03 include better support for template metaprogramming and enhancements to the Standard Template Library (STL). While it did not introduce major changes, C++03 laid the groundwork for future standards, such as C++11, which brought significant advancements to the language, including new features and performance improvements.