Lack of core function, and no sign of future updates in this case.
I'd also apply the term to other situations, such as a github page being taken down without any word from development about it, or similar.
Or, if an app is otherwise functional, but can't be installed/accessed via apk/app store (like the keyboard app swype that works fine, but you have to jump through hoops to install on newer android versions and is no longer listed in any store)