A neutral script is a script that is deliberately vague.  Or you might think of it as a blank canvas.  The dialogue could fit any number of situations, characters, relationships.  Its goal is to force actors to be specific in their on-stage choices, and to get them to make strong choices and to find a way to play them in a way an audience can see. They must first determine a set of given circumstances (where, what, why), and then they must create a character that can live in those circumstances.  This is work usually done with a partner, although the character work is a more solitary task.  The two actors must also agree on the relationship between the two characters.