A question with this tag is about non-public (aka private) iOS APIs. Apple will reject apps that use non-public APIs, but they can be distributed using ad-hoc or enterprise distribution (on jailed and jailbroken devices), or through jailbreaks. The main difference from software development standpoint of iOS private API that such APIs aren't declared in header files. As result extra steps are required to figure out API signature for its usage.
Questions with this tag discuss which private API can be used to accomplish different tasks, what are private API's signatures, runtime restrictions for usage of private API and so on.
The words "private API" in a question doesn't automatically make it suitable for this tag. As example, questions regarding Apple policies (why something was rejected or how do they know whether app uses some private API) aren't good fit for this tag. First of all, it's not purely software development question (it's more legal, tools questions). Second, all questions with this tag imply that it will be used in application which won't be submitted to Apple.
