This is the name given to a wife abandoned by her husband, as well as a wife whose husband has disappeared—a "straw widow." In this case, the woman is considered "bound," as freedom from the marriage can only be achieved with the death of her husband or by receiving a bill of divorce (get).
A husband abandoned by his wife or whose wife has disappeared is called an "agun." He is also considered "bound" according to the prohibition of polygamy established by Rabbeinu Gershom (965-1028): he cannot marry until he divorces his first wife or learns that she is no longer alive.