It is just like static linking in c. We can split code into different object files, and statically link to a big application. We help of header file, we can invert the dependency relationship to keep implementation private to keep autonomy. It also applies to node.js/web frontend application, here is a vite demo: https://github.com/taowen/vite-howto/tree/main/packages/STAT...
Would be better to provide a concrete example here.