Undocumented

Refers to features that are not described in the official documentation of a product. This lack of documentation can occur for a variety of reasons, including oversight. More often, though, undocumented features are features that were included because they were useful to the programmers developing the product but were deemed either unnecessary or potentially dangerous to end users. Undocumented features can also include untested features that will be officially supported in a future release of the product.