If "Abandoned" doesn't become a separate close-reason, we don't have to define it at all:
This question is unlikely to ever help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. See the FAQ.
A question, for instance, which describes a problem and - since it's abandoned - will never have a tested solution in an accepted answer, will not help future visitors. In most cases, the problem has gone away, or the user has solved the problem and simply didn't take the time to update their question (which is fine, by the way; People do as little or as much as they like).
These are a few criteria applying to abandoned questions which make it too localized:
- An out of date Ubuntu version is run by a small number of users
- The problem has been fixed after an update, virtually nobody will ever encounter this problem again - since the probability of you running the exact same revision of Ubuntu is minute
- The problem occurred because of unusual software or hardware, making the number of users who will be interested in the question even smaller yet.
- The issue has not been solved, but it doesn't affect anybody anymore, not even the OP. Which is evidenced by the fact that they don't respond to requests for information and so on.
In certain cases, I will close an abandoned question for any of the other close reasons if they apply.
In short: These comments people leave before they vote to close - "this question appears to be abandoned, ..." - are extremely helpful! But the question gets closed for the usual reason, we did not add a new close-reason, nor do we abuse the "too localized" reason for abandoned questions. In theory anyway.
In practice, we might very well be wrong about any specific question. If so, a flag to re-open from the OP will usually be enough to re-open the question. If I see that people are interested in or affected by the question, and it's within the scope of the FAQ, there is no reason not to re-open it, and it's easy to do so.