Word(s) to describe a set of things, which can't be empty

Solution 1:

As far as I know they're all called "electives" in English. Other languages, e.g. German, distinguish between

• mandatory elective (you have to choose n out of m, "Wahlpflichtfach")
• voluntary elective (you are free to choose none, some or all, "Wahlfach")

Solution 2:

A phrasing that may be of use to you in this context is elective requirements, conveying as it does that the choice of what exams to take is discretionary (elective), but there are minimum standards to be met (requirements).

Solution 3:

You wrote in your comment: It's a term used in a really long document. Also, when building user interfaces I need to keep it compact. In headers it appears as "Requirements for [adj] exams", or another one "students will be better informed to choose the right exams from the [adj] exams".

How about referring to the exams as chosen if the students have already chosen, "Requirements for chosen exams"

And if they have not already chosen, you could say offered exams.

"Students will be better informed about choosing the right exams from those offered."

I would hope the instructions make it very clear that they have to choose 2 or 3 of the offered exams.