Part of lp.app
Vocabularies that represent a set of content objects should be in this module. Those vocabularies that are only used for providing a UI are better placed in the browser code.
Note that you probably shouldn't be importing stuff from these modules, as it is better to have your schema's fields look up the vocabularies by name. Some of these vocabularies will only work if looked up by name, as they require context to calculate the available options. Obtaining a vocabulary by name also avoids circular import issues.
The binding of name -> class is done in the configure.zcml