I edited the excerpt for the tag wiki to use the following text:
This tag is for questions about modules hosted on Drupal.org. It should not be used to generally mean "this question is about a module," when the question is about a module's code, or when the question is already using a tag specific for the module, such as "views," "cck," or "pathauto."
Clearly, modules, and themes need to be limited in scope, or most of the questions, if not all, would used one of those. Excluding the tag for questions about module's code is essentially because in most of the cases using modules for those questions creates a false dichotomy: If the question, for example, is about using
drupal_add_js() in a module, the question is not different from using the same function in a theme's code.