What is הפקעת קידושין ? How does it work? And why is this not a good solution for an agunah (was I’ve heard..)
This is the concept of uprooting a marriage so that the bond is broken retroactively, and it is considered as though the couple was never married.
There are different means of achieving this result, but they are used rarely, both because it means that the couple were never married, and because they can only be done under specific circumstances.
For instance, in general the cooperation of the husband is essential for achieving the result (though there are exceptions to this rule), so that this is often not a good solution for women whose husbands refuse to give a Get.