Misunderstood exam question with consequences for incorrect answer

At my institution the default way to handle this is (3 Stick with the 0 for this question). Essentially, every student is required to handle the teaching language well enough to be able to work on the test. In practice, many teachers will fall back to (2 Give them some consolation points) if giving 0 points seems too harsh. If (1 Give them another stab at it with more language context) is an actual option, that seems like a senseful way, too (e.g., in a short verbal exam). However, in practice this is often not possible in my courses, either because it would be very impractical or because the course regulations do not allow it.

Both, (4 Grade the question they answered and not the question asked) and (5 Give him / her the lowest grade anyone else got for this question), seem like relatively weird ways to handle this situation. With (5), you are essentially decoupling the grades for the student from what (s)he has actually written on the test. (4) breaks a fundamental exam concept, i.e., that the instructor chooses the question that the student should be answering, and not vice versa.

As for this:

The student is on an important grade boundary and it could make a difference to their final grade even a difference to if they have to take the class again / can graduate on time / or even stay in the major.

As bad as you may feel if "your" grade is the tip of the iceberg that leads to bad consequences for the student, you should be aware that it is the sum of bad performances that has gotten the student into troubles. Your grade is just the last in a series, and your grade is as much "at fault" as any other bad grade the student received. Hence, I feel you are not required to take the larger picture into account.

Obvious zero points. The student didn't misread the question, but just didn't know the term. He or she made a wild guess at what it meant, and guessed wrong.

I have been grading exams for a long time (since 1988 or so), and it is not uncommon for a student who doesn't recognize a term to guess its meaning, and get it more or less wrong. Map generalization means (as I just googled) decreasing the level of detail on a map so that it remains uncluttered when its scale is reduced. That is a technical term from cartography, and something that I had to look up. I assume that by "general purpose map" you just mean a map that isn't specifically designed for a certain purpose. I didn't have to google that, and if you have no idea what map generalization means, it is not an entirely unreasonable guess that it has something to do with general-purpose maps.

(This answer may sound a bit arrogant, but I do have many years' experience trying to figure out, from a few hard-to-read words scribbled on a paper, not just if the answer is right or wrong, but if the student has understood the subject or not. Also, the only reason I am posting here right now is to get away from the exams waiting to be graded.)

Stick with the grade deserved for the question. I don't understand the concepts you're referring to, but I suggest the possibility that if the student had attended class regularly, then the student might have been aware that "map generalization" and "general purpose map" are two different things. You should not be surprised that poor attendance can impact an understanding of a topic in interesting ways.