What is a Banshee?

From my novel Freedom's Banshee:

Look up the term BANSHEE and you will come back with several different definitions. For the purposes of this book, the term refers to a spirit or apparition (Usually a pretty female) that appears at the side of a warrior that has fallen in the field of battle. She appears to clean the warrior’s armor, his cloths, and his body before he goes into the hereafter.