When a woman dies alone, beyond the reach of any help-usually in a wetland or forest-she may come back as a Banshee, similar to a Specter. A Banshee's shriek is a portent of impending tragedy: A member of the household of the person who heard it will soon die. If visible, the Banshee will take the form of the person so doomed. There is evidence that stories of banshees are simply fox calls: a fox can make an absolutely horrific screech (and matching facial expression) if it sees fit.
If paired with the Mass Effect tag, it refers to a Reaper-corrupted version of an Asari.