Metaprogramming refers to code that operates on other code as if it were data. It can take code in as parameters, reflect over it, inspect it, create it, modify it, and return it. Static metaprogramming means doing that work at compile-time, and typically modifying or adding to the program based on that work.

Today it is possible to do static metaprogramming completely outside of the language - using packages such as build_runner to generate code and using the analyzer apis for introspection. These separate tools however are not well integrated into the compilers or tools, and it adds a lot of complexity where this is done. It also tends to be slower than an integrated solution because it can't share any work with the compiler.