A package in Python is indeed a group of related modules, which means that option B is correct. Python packages are not single files ending with the .pa extension, so option A is incorrect. The __name__ variable typically contains the name of a module, not a package, making option C incorrect. The .pyc extension is used to mark compiled Python files (not semi-compiled), which can be considered as semi-compiled in the sense that they are not source files but byte-compiled files. Therefore, option D is correct.